<?php
/**
 * A single database record & abstract class for the data-access-model.
 *
 * <h2>Extensions and Decorators</h2>
 *
 * See {@link Extension} and {@link DataObjectDecorator}.
 * 
 * <h2>Permission Control</h2>
 * 
 * Object-level access control by {@link Permission}. Permission codes are arbitrary
 * strings which can be selected on a group-by-group basis.
 * 
 * <code>
 * class Article extends DataObject implements PermissionProvider {
 * 	static $api_access = true;
 * 	
 * 	public function canView($member = false) {
 * 		return Permission::check('ARTICLE_VIEW');
 * 	}
 * 	public function canEdit($member = false) {
 * 		return Permission::check('ARTICLE_EDIT');
 * 	}
 * 	public function canDelete() {
 * 		return Permission::check('ARTICLE_DELETE');
 * 	}
 * 	public function canCreate() {
 * 		return Permission::check('ARTICLE_CREATE');
 * 	}
 * 	public function providePermissions() {
 * 		return array(
 * 			'ARTICLE_VIEW' => 'Read an article object',
 * 			'ARTICLE_EDIT' => 'Edit an article object',
 * 			'ARTICLE_DELETE' => 'Delete an article object',
 * 			'ARTICLE_CREATE' => 'Create an article object',
 * 		);
 * 	}
 * }
 * </code> 
 *
 * Object-level access control by {@link Group} membership: 
 * <code>
 * class Article extends DataObject {
 * 	static $api_access = true;
 * 	
 * 	public function canView($member = false) {
 * 		if(!$member) $member = Member::currentUser();
 *		return $member->inGroup('Subscribers');
 * 	}
 * 	public function canEdit($member = false) {
 * 		if(!$member) $member = Member::currentUser();
 *		return $member->inGroup('Editors');
 * 	}
 * 	
 * 	// ...
 * }
 * </code>
 * 
 * If any public method on this class is prefixed with an underscore, 
 * the results are cached in memory through {@link cachedCall()}.
 * 
 * 
 * @todo Add instance specific removeExtension() which undos loadExtraStatics()
 *  and defineMethods()
 * 
 * @package sapphire
 * @subpackage model
 */
class DataObject extends ViewableData implements DataObjectInterface, i18nEntityProvider {
	
	/**
	 * Human-readable singular name.
	 * @var string
	 */
	public static $singular_name = null;
	
	/**
	 * Human-readable pluaral name
	 * @var string
	 */
	public static $plural_name = null;
	
	/**
	 * Allow API access to this object?
	 * @todo Define the options that can be set here
	 */
	public static $api_access = false;
	
	public static
		$cache_has_own_table       = array(),
		$cache_has_own_table_field = array();
	
	/**
	 * True if this DataObject has been destroyed.
	 * @var boolean
	 */
	public $destroyed = false;
	
	/**
	 * Data stored in this objects database record. An array indexed
	 * by fieldname.
	 * @var array
	 */
	protected $record;

	/**
	 * An array indexed by fieldname, true if the field has been changed.
	 * Use {@link getChangedFields()} and {@link isChanged()} to inspect
	 * the changed state.
	 * 
	 * @var array
	 */
	private $changed;

	/**
	 * The database record (in the same format as $record), before
	 * any changes.
	 * @var array
	 */
	protected $original;

	/**
	 * The one-to-one, one-to-many and many-to-one components
	 * indexed by component name.
	 * @var array
	 */
	protected $components;
	
	/**
	 * Used by onBeforeDelete() to ensure child classes call parent::onBeforeDelete()
	 * @var boolean
	 */
	protected $brokenOnDelete = false;
	
	/**
	 * Used by onBeforeWrite() to ensure child classes call parent::onBeforeWrite()
	 * @var boolean
	 */
	protected $brokenOnWrite = false;
	
	/**
	 * Should dataobjects be validated before they are written?
	 */
	private static $validation_enabled = true;
	
	/**
	 * Returns when validation on DataObjects is enabled.
	 * @return bool
	 */
	static function get_validation_enabled() {
		return self::$validation_enabled;
	}
	
	/**
	 * Set whether DataObjects should be validated before they are written.
	 * @param $enable bool
	 * @see DataObject::validate()
	 */
	static function set_validation_enabled($enable) {
		self::$validation_enabled = (bool) $enable;
	}

	/**
	 * Return the complete map of fields on this object, including Created, LastEdited and ClassName
	 *
	 * @param string $class
	 * @return array
	 */
	public static function database_fields($class) {
		if(get_parent_class($class) == 'DataObject') {
			return array_merge (
				array (
					'ClassName'  => "Enum('" . implode(', ', ClassInfo::subclassesFor($class)) . "')",
					'Created'    => 'SS_Datetime',
					'LastEdited' => 'SS_Datetime'
				),
				self::custom_database_fields($class)
			);
		}

		return self::custom_database_fields($class);
	}

	/**
	 * Get all database columns explicitly defined on a class in {@link DataObject::$db} 
	 * and {@link DataObject::$has_one}. Resolves instances of {@link CompositeDBField} 
	 * into the actual database fields, rather than the name of the field which 
	 * might not equate a database column.
	 * 
	 * @uses CompositeDBField->compositeDatabaseFields()
	 *
	 * @param string $class
	 * @return array Map of fieldname to specification, similiar to {@link DataObject::$db}.
	 */
	public static function custom_database_fields($class) {
		$fields = Object::uninherited_static($class, 'db');
		
		foreach(self::composite_fields($class, false) as $fieldName => $fieldClass) {
			// Remove the original fieldname, its not an actual database column
			unset($fields[$fieldName]);
			
			// Add all composite columns
			$compositeFields = singleton($fieldClass)->compositeDatabaseFields();
			if($compositeFields) foreach($compositeFields as $compositeName => $spec) {
				$fields["{$fieldName}{$compositeName}"] = $spec;
			}
		}
		
		// Add has_one relationships
		$hasOne = Object::uninherited_static($class, 'has_one');
		if($hasOne) foreach(array_keys($hasOne) as $field) {
			$fields[$field . 'ID'] = 'ForeignKey';
		}
		
		return (array)$fields;
	}
	
	private static $_cache_custom_database_fields = array();
	
	
	/**
	 * Returns the field class if the given db field on the class is a composite field.
	 * Will check all applicable ancestor classes and aggregate results.
	 */
	static function is_composite_field($class, $name, $aggregated = true) {
		if(!isset(self::$_cache_composite_fields[$class])) self::cache_composite_fields($class);
		
		if(isset(self::$_cache_composite_fields[$class][$name])) {
			return self::$_cache_composite_fields[$class][$name];
			
		} else if($aggregated && $class != 'DataObject' && ($parentClass=get_parent_class($class)) != 'DataObject') {
			return self::is_composite_field($parentClass, $name);
		}
	}

	/**
	 * Returns a list of all the composite if the given db field on the class is a composite field.
	 * Will check all applicable ancestor classes and aggregate results.
	 */
	static function composite_fields($class, $aggregated = true) {
		if(!isset(self::$_cache_composite_fields[$class])) self::cache_composite_fields($class);
		
		$compositeFields = self::$_cache_composite_fields[$class];
		
		if($aggregated && $class != 'DataObject' && ($parentClass=get_parent_class($class)) != 'DataObject') {
			$compositeFields = array_merge($compositeFields, 
				self::composite_fields($parentClass));
		}
		
		return $compositeFields;
	}

	/**
	 * Internal cacher for the composite field information
	 */
	private static function cache_composite_fields($class) {
		$compositeFields = array();
		
		$fields = Object::uninherited_static($class, 'db');
		if($fields) foreach($fields as $fieldName => $fieldClass) {
			// Strip off any parameters
			$bPos = strpos('(', $fieldClass);
			if($bPos !== FALSE) $fieldClass = substr(0,$bPos, $fieldClass);
			
			// Test to see if it implements CompositeDBField
			if(ClassInfo::classImplements($fieldClass, 'CompositeDBField')) {
				$compositeFields[$fieldName] = $fieldClass;
			}
		}
		
		self::$_cache_composite_fields[$class] = $compositeFields;
	}
	
	private static $_cache_composite_fields = array();
	

	/**
	 * Construct a new DataObject.
	 *
	 * @param array|null $record This will be null for a new database record.  Alternatively, you can pass an array of
	 * field values.  Normally this contructor is only used by the internal systems that get objects from the database.
	 * @param boolean $isSingleton This this to true if this is a singleton() object, a stub for calling methods.  Singletons
	 * don't have their defaults set.
	 */
	function __construct($record = null, $isSingleton = false) {
		// Set the fields data.
		if(!$record) {
			$record = array(
				'ID' => 0,
				'ClassName' => get_class($this),
				'RecordClassName' => get_class($this)
			);
		}

		if(!is_array($record)) {
			if(is_object($record)) $passed = "an object of type '$record->class'";
			else $passed = "The value '$record'";

			user_error("DataObject::__construct passed $passed.  It's supposed to be passed an array,
			taken straight from the database.  Perhaps you should use DataObject::get_one instead?", E_USER_WARNING);
			$record = null;
		}

		// Convert PostgreSQL boolean values
		// TODO: Implement this more elegantly, for example by writing a more intelligent SQL SELECT query prior to object construction
		if(DB::getConn() instanceof PostgreSQLDatabase) {
			$this->class = get_class($this);
			foreach($record as $k => $v) {
				if($this->db($k) == 'Boolean' && $v == 'f') $record[$k] = '0';
			}
		}
		
		// TODO: MSSQL has a convert function that can do this on the SQL end. We just need a
		// nice way of telling the database how we want to get the value out on a per-fieldtype basis
		if(DB::getConn() instanceof MSSQLDatabase) {
			$this->class = get_class($this);
			foreach($record as $k => $v) {
				if($v) {
					if($k == 'Created' || $k == 'LastEdited') {
						$fieldtype = 'SS_Datetime';
					} else {
						$fieldtype = $this->db($k);
					}
				
					// MSSQLDatabase::date() uses datetime for the data type for "Date" and "SS_Datetime"
					switch($fieldtype) {
						case "Date":
							$v = preg_replace('/:[0-9][0-9][0-9]([ap]m)$/i', ' \\1', $v);
							$record[$k] = date('Y-m-d', strtotime($v));
							break;
					
						case "Datetime":
						case "SS_Datetime":
							$v = preg_replace('/:[0-9][0-9][0-9]([ap]m)$/i', ' \\1', $v);
							$record[$k] = date('Y-m-d H:i:s', strtotime($v));
							break;
					}
				}
			}
		}

		// Set $this->record to $record, but ignore NULLs
		$this->record = array();
		foreach($record as $k => $v) {
			// Ensure that ID is stored as a number and not a string
			// To do: this kind of clean-up should be done on all numeric fields, in some relatively
			// performant manner
			if($v !== null) {
				if($k == 'ID' && is_numeric($v)) $this->record[$k] = (int)$v;
				else $this->record[$k] = $v;
			}
		}
		$this->original = $this->record;

		// Keep track of the modification date of all the data sourced to make this page
		// From this we create a Last-Modified HTTP header
		if(isset($record['LastEdited'])) {
			HTTP::register_modification_date($record['LastEdited']);
		}

		parent::__construct();

		// Must be called after parent constructor
		if(!$isSingleton && (!isset($this->record['ID']) || !$this->record['ID'])) {
			$this->populateDefaults();
		}

		// prevent populateDefaults() and setField() from marking overwritten defaults as changed
		$this->changed = array();
	}

	/**
	 * Destroy all of this objects dependant objects.
	 * You'll need to call this to get the memory of an object that has components or extensions freed.
	 */
	function destroy() {
		$this->extension_instances = null;
		$this->components = null;
		$this->destroyed = true;
		$this->record = null;
		$this->original = null;
		$this->changed = null;
		$this->flushCache(false);
	}

	/**
	 * Create a duplicate of this node.
	 * Caution: Doesn't duplicate relations.
	 *
	 * @param $doWrite Perform a write() operation before returning the object.  If this is true, it will create the duplicate in the database.
	 * @return DataObject A duplicate of this node. The exact type will be the type of this node.
	 */
	function duplicate($doWrite = true) {
		$className = $this->class;
		$clone = new $className( $this->record );
		$clone->ID = 0;
		if($doWrite) $clone->write();
		return $clone;
	}

	/**
	 * Set the ClassName attribute. {@link $class} is also updated.
	 * Warning: This will produce an inconsistent record, as the object
	 * instance will not automatically switch to the new subclass.
	 * Please use {@link newClassInstance()} for this purpose,
	 * or destroy and reinstanciate the record.
	 *
	 * @param string $className The new ClassName attribute (a subclass of {@link DataObject})
	 */
	function setClassName($className) {
		$className = trim($className);
		if(!$className || !is_subclass_of($className, 'DataObject')) return;

		$this->class = $className;
		$this->setField("ClassName", $className);
	}

	/**
	 * Create a new instance of a different class from this object's record.
	 * This is useful when dynamically changing the type of an instance. Specifically,
	 * it ensures that the instance of the class is a match for the className of the
	 * record. Don't set the {@link DataObject->class} or {@link DataObject->ClassName}
	 * property manually before calling this method, as it will confuse change detection.
	 * 
	 * If the new class is different to the original class, defaults are populated again
	 * because this will only occur automatically on instantiation of a DataObject if
	 * there is no record, or the record has no ID. In this case, we do have an ID but
	 * we still need to repopulate the defaults.
	 *
	 * @param string $newClassName The name of the new class
	 *
	 * @return DataObject The new instance of the new class, The exact type will be of the class name provided.
	 */
	function newClassInstance($newClassName) {
		$originalClass = $this->ClassName;
		$newInstance = new $newClassName(array_merge(
			$this->record,
			array(
				'ClassName' => $originalClass,
				'RecordClassName' => $originalClass,
			)
		));
		
		if($newClassName != $originalClass) {
			$newInstance->setClassName($newClassName);
			$newInstance->populateDefaults();
			$newInstance->forceChange();
		}

		return $newInstance;
	}

	/**
	 * Adds methods from the extensions.
	 * Called by Object::__construct() once per class.
	 */
	function defineMethods() {
		parent::defineMethods();

		// Define the extra db fields - this is only necessary for extensions added in the
		// class definition.  Object::add_extension() will call this at definition time for
		// those objects, which is a better mechanism.  Perhaps extensions defined inside the
		// class def can somehow be applied at definiton time also?
		if($this->extension_instances) foreach($this->extension_instances as $i => $instance) {
			if(!$instance->class) {
				$class = get_class($instance);
				user_error("DataObject::defineMethods(): Please ensure {$class}::__construct() calls parent::__construct()", E_USER_ERROR);
			}
		}

		if($this->class == 'DataObject') return;

		// Set up accessors for joined items
		if($manyMany = $this->many_many()) {
			foreach($manyMany as $relationship => $class) {
				$this->addWrapperMethod($relationship, 'getManyManyComponents');
			}
		}
		if($hasMany = $this->has_many()) {

			foreach($hasMany as $relationship => $class) {
				$this->addWrapperMethod($relationship, 'getComponents');
			}

		}
		if($hasOne = $this->has_one()) {
			foreach($hasOne as $relationship => $class) {
				$this->addWrapperMethod($relationship, 'getComponent');
			}
		}
		if($belongsTo = $this->belongs_to()) foreach(array_keys($belongsTo) as $relationship) {
			$this->addWrapperMethod($relationship, 'getComponent');
		}
	}

	/**
	 * Returns true if this object "exists", i.e., has a sensible value.
	 * The default behaviour for a DataObject is to return true if
	 * the object exists in the database, you can override this in subclasses.
	 *
	 * @return boolean true if this object exists
	 */
	public function exists() {
		return ($this->record && $this->record['ID'] > 0);
	}

	public function isEmpty(){
		$isEmpty = true;
		if($this->record){
			foreach($this->record as $k=>$v){
				if($k != "ID"){
					$isEmpty = $isEmpty && !$v;
				}
			}
		}
		return $isEmpty;
	}

	/**
	 * Get the user friendly singular name of this DataObject.
	 * If the name is not defined (by redefining $singular_name in the subclass),
	 * this returns the class name.
	 *
	 * @return string User friendly singular name of this DataObject
	 */
	function singular_name() {
		if(!$name = $this->stat('singular_name')) {
			$name = ucwords(trim(strtolower(preg_replace('/_?([A-Z])/', ' $1', $this->class))));
		}
		
		return $name;
	}

	/**
	 * Get the translated user friendly singular name of this DataObject
	 * same as singular_name() but runs it through the translating function
	 *
	 * Translating string is in the form:
	 *     $this->class.SINGULARNAME
	 * Example:
	 *     Page.SINGULARNAME
	 *
	 * @return string User friendly translated singular name of this DataObject
	 */
	function i18n_singular_name() {
		return _t($this->class.'.SINGULARNAME', $this->singular_name());
	}

	/**
	 * Get the user friendly plural name of this DataObject
	 * If the name is not defined (by renaming $plural_name in the subclass),
	 * this returns a pluralised version of the class name.
	 *
	 * @return string User friendly plural name of this DataObject
	 */
	function plural_name() {
		if($name = $this->stat('plural_name')) {
			return $name;
		} else {
			$name = $this->singular_name();
			if(substr($name,-1) == 'e') $name = substr($name,0,-1);
			else if(substr($name,-1) == 'y') $name = substr($name,0,-1) . 'ie';

			return ucfirst($name . 's');
		}
	}

	/**
	 * Get the translated user friendly plural name of this DataObject
	 * Same as plural_name but runs it through the translation function
	 * Translation string is in the form:
	 *      $this->class.PLURALNAME
	 * Example:
	 *      Page.PLURALNAME
	 *
	 * @return string User friendly translated plural name of this DataObject
	 */
	function i18n_plural_name()
	{
		$name = $this->plural_name();
		return _t($this->class.'.PLURALNAME', $name);
	}
	
	/**
	 * Standard implementation of a title/label for a specific
	 * record. Tries to find properties 'Title' or 'Name',
	 * and falls back to the 'ID'. Useful to provide
	 * user-friendly identification of a record, e.g. in errormessages
	 * or UI-selections.
	 * 
	 * Overload this method to have a more specialized implementation,
	 * e.g. for an Address record this could be:
	 * <code>
	 * public function getTitle() {
	 *   return "{$this->StreetNumber} {$this->StreetName} {$this->City}";
	 * }
	 * </code>
	 *
	 * @return string
	 */
	public function getTitle() {
		if($this->hasDatabaseField('Title')) return $this->getField('Title');
		if($this->hasDatabaseField('Name')) return $this->getField('Name');
		
		return "#{$this->ID}";
	}

	/**
	 * Returns the associated database record - in this case, the object itself.
	 * This is included so that you can call $dataOrController->data() and get a DataObject all the time.
	 *
	 * @return DataObject Associated database record
	 */
	public function data() {
		return $this;
	}

	/**
	 * Convert this object to a map.
	 *
	 * @return array The data as a map.
	 */
	public function toMap() {
		return $this->record;
	}

	/**
	 * Update a number of fields on this object, given a map of the desired changes.
	 * 
	 * The field names can be simple names, or you can use a dot syntax to access $has_one relations.
	 * For example, array("Author.FirstName" => "Jim") will set $this->Author()->FirstName to "Jim".
	 * 
	 * update() doesn't write the main object, but if you use the dot syntax, it will write() 
	 * the related objects that it alters.
	 *
	 * @param array $data A map of field name to data values to update.
	 */
	public function update($data) {
		foreach($data as $k => $v) {
			// Implement dot syntax for updates
			if(strpos($k,'.') !== false) {
				$relations = explode('.', $k);
				$fieldName = array_pop($relations);
				$relObj = $this;
				foreach($relations as $i=>$relation) {
					// no support for has_many or many_many relationships,
					// as the updater wouldn't know which object to write to (or create)
					if($relObj->$relation() instanceof DataObject) {
						$relObj = $relObj->$relation();
						
						// If the intermediate relationship objects have been created, then write them
						if($i<sizeof($relation)-1 && !$relObj->ID) $relObj->write();
					} else {
						user_error(
							"DataObject::update(): Can't traverse relationship '$relation'," .  
							"it has to be a has_one relationship or return a single DataObject", 
							E_USER_NOTICE
						);
						// unset relation object so we don't write properties to the wrong object
						unset($relObj);
						break;
					}
				}

				if($relObj) {
					$relObj->$fieldName = $v;
					$relObj->write();
					$relObj->flushCache();
				} else {
					user_error("Couldn't follow dot syntax '$k' on '$this->class' object", E_USER_WARNING);
				}
			} else {
				$this->$k = $v;
			}
		}
	}
	
	/**
	 * Pass changes as a map, and try to
	 * get automatic casting for these fields.
	 * Doesn't write to the database. To write the data,
	 * use the write() method.
	 *
	 * @param array $data A map of field name to data values to update.
	 */
	public function castedUpdate($data) {
		foreach($data as $k => $v) {
			$this->setCastedField($k,$v);
		}
	}

	/**
	 * Merges data and relations from another object of same class,
	 * without conflict resolution. Allows to specify which
	 * dataset takes priority in case its not empty.
	 * has_one-relations are just transferred with priority 'right'.
	 * has_many and many_many-relations are added regardless of priority.
	 *
	 * Caution: has_many/many_many relations are moved rather than duplicated,
	 * meaning they are not connected to the merged object any longer.
	 * Caution: Just saves updated has_many/many_many relations to the database,
	 * doesn't write the updated object itself (just writes the object-properties).
	 * Caution: Does not delete the merged object.
	 * Caution: Does now overwrite Created date on the original object.
	 *
	 * @param $obj DataObject
	 * @param $priority String left|right Determines who wins in case of a conflict (optional)
	 * @param $includeRelations Boolean Merge any existing relations (optional)
	 * @param $overwriteWithEmpty Boolean Overwrite existing left values with empty right values.
	 * 	Only applicable with $priority='right'. (optional)
	 * @return Boolean
	 */
	public function merge($rightObj, $priority = 'right', $includeRelations = true, $overwriteWithEmpty = false) {
		$leftObj = $this;

		if($leftObj->ClassName != $rightObj->ClassName) {
			// we can't merge similiar subclasses because they might have additional relations
			user_error("DataObject->merge(): Invalid object class '{$rightObj->ClassName}'
			(expected '{$leftObj->ClassName}').", E_USER_WARNING);
			return false;
		}

		if(!$rightObj->ID) {
			user_error("DataObject->merge(): Please write your merged-in object to the database before merging,
				to make sure all relations are transferred properly.').", E_USER_WARNING);
			return false;
		}

		// makes sure we don't merge data like ID or ClassName
		$leftData = $leftObj->inheritedDatabaseFields();
		$rightData = $rightObj->inheritedDatabaseFields();

		foreach($rightData as $key=>$rightVal) {
			// don't merge conflicting values if priority is 'left'
			if($priority == 'left' && $leftObj->{$key} !== $rightObj->{$key}) continue;

			// don't overwrite existing left values with empty right values (if $overwriteWithEmpty is set)
			if($priority == 'right' && !$overwriteWithEmpty && empty($rightObj->{$key})) continue;

			// TODO remove redundant merge of has_one fields
			$leftObj->{$key} = $rightObj->{$key};
		}

		// merge relations
		if($includeRelations) {
			if($manyMany = $this->many_many()) {
				foreach($manyMany as $relationship => $class) {
					$leftComponents = $leftObj->getManyManyComponents($relationship);
					$rightComponents = $rightObj->getManyManyComponents($relationship);
					if($rightComponents && $rightComponents->exists()) $leftComponents->addMany($rightComponents->column('ID'));
					$leftComponents->write();
				}
			}

			if($hasMany = $this->has_many()) {
				foreach($hasMany as $relationship => $class) {
					$leftComponents = $leftObj->getComponents($relationship);
					$rightComponents = $rightObj->getComponents($relationship);
					if($rightComponents && $rightComponents->exists()) $leftComponents->addMany($rightComponents->column('ID'));
					$leftComponents->write();
				}

			}

			if($hasOne = $this->has_one()) {
				foreach($hasOne as $relationship => $class) {
					$leftComponent = $leftObj->getComponent($relationship);
					$rightComponent = $rightObj->getComponent($relationship);
					if($leftComponent->exists() && $rightComponent->exists() && $priority == 'right') {
						$leftObj->{$relationship . 'ID'} = $rightObj->{$relationship . 'ID'};
					}
				}
			}
		}

		return true;
	}

	/**
	 * Forces the record to think that all its data has changed.
	 * Doesn't write to the database. Only sets fields as changed
	 * if they are not already marked as changed.
	 */
	public function forceChange() {
		// $this->record might not contain the blank values so we loop on $this->inheritedDatabaseFields() as well
		$fieldNames = array_unique(array_merge(array_keys($this->record), array_keys($this->inheritedDatabaseFields())));
		
		foreach($fieldNames as $fieldName) {
			if(!isset($this->changed[$fieldName])) $this->changed[$fieldName] = 1;
			// Populate the null values in record so that they actually get written
			if(!isset($this->record[$fieldName])) $this->record[$fieldName] = null;
		}
		
		// @todo Find better way to allow versioned to write a new version after forceChange
		if($this->isChanged('Version')) unset($this->changed['Version']);
	}
	
	/**
	 * Validate the current object.
	 *
	 * By default, there is no validation - objects are always valid!  However, you can overload this method in your
	 * DataObject sub-classes to specify custom validation.
	 * 
	 * Invalid objects won't be able to be written - a warning will be thrown and no write will occur.  onBeforeWrite()
	 * and onAfterWrite() won't get called either.
	 * 
	 * It is expected that you call validate() in your own application to test that an object is valid before attempting
	 * a write, and respond appropriately if it isnt'.
	 * 
	 * @return A {@link ValidationResult} object
	 */
	protected function validate() {
		return new ValidationResult();
	}

	/**
	 * Event handler called before writing to the database.
	 * You can overload this to clean up or otherwise process data before writing it to the
	 * database.  Don't forget to call parent::onBeforeWrite(), though!
	 *
	 * This called after {@link $this->validate()}, so you can be sure that your data is valid.
	 * 
	 * @uses DataObjectDecorator->onBeforeWrite()
	 */
	protected function onBeforeWrite() {
		$this->brokenOnWrite = false;
		
		$dummy = null;
		$this->extend('onBeforeWrite', $dummy);
	}

	/**
	 * Event handler called after writing to the database.
	 * You can overload this to act upon changes made to the data after it is written.
	 * $this->changed will have a record
	 * database.  Don't forget to call parent::onAfterWrite(), though!
	 *
	 * @uses DataObjectDecorator->onAfterWrite()
	 */
	protected function onAfterWrite() {
		$dummy = null;
		$this->extend('onAfterWrite', $dummy);
	}

	/**
	 * Event handler called before deleting from the database.
	 * You can overload this to clean up or otherwise process data before delete this
	 * record.  Don't forget to call parent::onBeforeDelete(), though!
	 *
	 * @uses DataObjectDecorator->onBeforeDelete()
	 */
	protected function onBeforeDelete() {
		$this->brokenOnDelete = false;
		
		$dummy = null;
		$this->extend('onBeforeDelete', $dummy);
	}
	
	protected function onAfterDelete() {
		$this->extend('onAfterDelete');
	}

	/**
	 * Load the default values in from the self::$defaults array.
	 * Will traverse the defaults of the current class and all its parent classes.
	 * Called by the constructor when creating new records.
	 * 
	 *  @uses DataObjectDecorator->populateDefaults()
	 */
	public function populateDefaults() {
		$classes = array_reverse(ClassInfo::ancestry($this));
		
		foreach($classes as $class) {
			$defaults = Object::uninherited_static($class, 'defaults');
			
			if($defaults && !is_array($defaults)) {
				user_error("Bad '$this->class' defaults given: " . var_export($defaults, true),
				 	E_USER_WARNING);
				$defaults = null;
			}
			
			if($defaults) foreach($defaults as $fieldName => $fieldValue) {
				// SRM 2007-03-06: Stricter check
				if(!isset($this->$fieldName) || $this->$fieldName === null) {
					$this->$fieldName = $fieldValue;
				}
				// Set many-many defaults with an array of ids
				if(is_array($fieldValue) && $this->many_many($fieldName)) {
					$manyManyJoin = $this->$fieldName();
					$manyManyJoin->setByIdList($fieldValue);
				}
			}
			if($class == 'DataObject') {
				break;
			}
		}
		
		$this->extend('populateDefaults');
	}

	/**
	 * Writes all changes to this object to the database.
	 *  - It will insert a record whenever ID isn't set, otherwise update.
	 *  - All relevant tables will be updated.
	 *  - $this->onBeforeWrite() gets called beforehand.
	 *  - Extensions such as Versioned will ammend the database-write to ensure that a version is saved.
	 *  - Calls to {@link DataObjectLog} can be used to see everything that's been changed.
	 * 
	 *  @uses DataObjectDecorator->augmentWrite()
	 *
	 * @param boolean $showDebug Show debugging information
	 * @param boolean $forceInsert Run INSERT command rather than UPDATE, even if record already exists
	 * @param boolean $forceWrite Write to database even if there are no changes
	 * @param boolean $writeComponents Call write() on all associated component instances which were previously
	 * 					retrieved through {@link getComponent()}, {@link getComponents()} or {@link getManyManyComponents()}
	 * 					(Default: false)
	 *
	 * @return int The ID of the record
	 * @throws ValidationException Exception that can be caught and handled by the calling function
	 */
	public function write($showDebug = false, $forceInsert = false, $forceWrite = false, $writeComponents = false) {
		$firstWrite = false;
		$this->brokenOnWrite = true;
		$isNewRecord = false;
		
		if(self::get_validation_enabled()) {
			$valid = $this->validate();
			if(!$valid->valid()) {
				// Used by DODs to clean up after themselves, eg, Versioned
				$this->extend('onAfterSkippedWrite');
				throw new ValidationException($valid, "Validation error writing a $this->class object: " . $valid->message() . ".  Object not written.", E_USER_WARNING);
				return false;
			}
		}

		$this->onBeforeWrite();
		if($this->brokenOnWrite) {
			user_error("$this->class has a broken onBeforeWrite() function.  Make sure that you call parent::onBeforeWrite().", E_USER_ERROR);
		}

		// New record = everything has changed

		if(($this->ID && is_numeric($this->ID)) && !$forceInsert) {
			$dbCommand = 'update';

			// Update the changed array with references to changed obj-fields
			foreach($this->record as $k => $v) {
				if(is_object($v) && method_exists($v, 'isChanged') && $v->isChanged()) {
					$this->changed[$k] = true;
				}
			}

		} else{
			$dbCommand = 'insert';

			$this->changed = array();
			foreach($this->record as $k => $v) {
				$this->changed[$k] = 2;
			}
			
			$firstWrite = true;
		}

		// No changes made
		if($this->changed) {
			foreach($this->getClassAncestry() as $ancestor) {
				if(self::has_own_table($ancestor))
				$ancestry[] = $ancestor;
			}

			// Look for some changes to make
			if(!$forceInsert) unset($this->changed['ID']);

			$hasChanges = false;
			foreach($this->changed as $fieldName => $changed) {
				if($changed) {
					$hasChanges = true;
					break;
				}
			}

			if($hasChanges || $forceWrite || !$this->record['ID']) {
					
				// New records have their insert into the base data table done first, so that they can pass the
				// generated primary key on to the rest of the manipulation
				$baseTable = $ancestry[0];
				
				if((!isset($this->record['ID']) || !$this->record['ID']) && isset($ancestry[0])) {	

					DB::query("INSERT INTO \"{$baseTable}\" (\"Created\") VALUES (" . DB::getConn()->now() . ")");
					$this->record['ID'] = DB::getGeneratedID($baseTable);
					$this->changed['ID'] = 2;

					$isNewRecord = true;
				}

				// Divvy up field saving into a number of database manipulations
				$manipulation = array();
				if(isset($ancestry) && is_array($ancestry)) {
					foreach($ancestry as $idx => $class) {
						$classSingleton = singleton($class);
						
						foreach($this->record as $fieldName => $fieldValue) {
							if(isset($this->changed[$fieldName]) && $this->changed[$fieldName] && $fieldType = $classSingleton->hasOwnTableDatabaseField($fieldName)) {
								$fieldObj = $this->dbObject($fieldName);
								if(!isset($manipulation[$class])) $manipulation[$class] = array();

								// if database column doesn't correlate to a DBField instance...
								if(!$fieldObj) {
									$fieldObj = DBField::create('Varchar', $this->record[$fieldName], $fieldName);
								}

								// Both CompositeDBFields and regular fields need to be repopulated
								$fieldObj->setValue($this->record[$fieldName], $this->record);

								if($class != $baseTable || $fieldName!='ID')
									$fieldObj->writeToManipulation($manipulation[$class]);
							}
						}

						// Add the class name to the base object
						if($idx == 0) {
							$manipulation[$class]['fields']["LastEdited"] = "'".SS_Datetime::now()->Rfc2822()."'";
							if($dbCommand == 'insert') {
								$manipulation[$class]['fields']["Created"] = "'".SS_Datetime::now()->Rfc2822()."'";
								//echo "<li>$this->class - " .get_class($this);
								$manipulation[$class]['fields']["ClassName"] = "'$this->class'";
							}
						}

						// In cases where there are no fields, this 'stub' will get picked up on
						if(self::has_own_table($class)) {
							$manipulation[$class]['command'] = $dbCommand;
							$manipulation[$class]['id'] = $this->record['ID'];
						} else {
							unset($manipulation[$class]);
						}
					}
				}
				$this->extend('augmentWrite', $manipulation);
				
				// New records have their insert into the base data table done first, so that they can pass the
				// generated ID on to the rest of the manipulation
				if(isset($isNewRecord) && $isNewRecord && isset($manipulation[$baseTable])) {
					$manipulation[$baseTable]['command'] = 'update';
				}
				
				DB::manipulate($manipulation);

				if(isset($isNewRecord) && $isNewRecord) {
					DataObjectLog::addedObject($this);
				} else {
					DataObjectLog::changedObject($this);
				}
				
				$this->onAfterWrite();

				$this->changed = null;
			} elseif ( $showDebug ) {
				echo "<b>Debug:</b> no changes for DataObject<br />";
				// Used by DODs to clean up after themselves, eg, Versioned
				$this->extend('onAfterSkippedWrite');
			}

			// Clears the cache for this object so get_one returns the correct object.
			$this->flushCache();

			if(!isset($this->record['Created'])) {
				$this->record['Created'] = SS_Datetime::now()->Rfc2822();
			}
			$this->record['LastEdited'] = SS_Datetime::now()->Rfc2822();
		} else {
			// Used by DODs to clean up after themselves, eg, Versioned
			$this->extend('onAfterSkippedWrite');
		}

		// Write ComponentSets as necessary
		if($writeComponents) {
			$this->writeComponents(true);
		}
		return $this->record['ID'];
	}


	/**
	 * Write the cached components to the database. Cached components could refer to two different instances of the same record.
	 * 
	 * @param $recursive Recursively write components
	 */
	public function writeComponents($recursive = false) {
		if(!$this->components) return;
		
		foreach($this->components as $component) {
			$component->write(false, false, false, $recursive);
		}
	}
	
	/**
	 * Perform a write without affecting the version table.
	 * On objects without versioning.
	 *
	 * @return int The ID of the record
	 */
	public function writeWithoutVersion() {
		$this->changed['Version'] = 1;
		if(!isset($this->record['Version'])) {
			$this->record['Version'] = -1;
		}
		return $this->write();
	}

	/**
	 * Delete this data object.
	 * $this->onBeforeDelete() gets called.
	 * Note that in Versioned objects, both Stage and Live will be deleted.
	 *  @uses DataObjectDecorator->augmentSQL()
	 */
	public function delete() {
		$this->brokenOnDelete = true;
		$this->onBeforeDelete();
		if($this->brokenOnDelete) {
			user_error("$this->class has a broken onBeforeDelete() function.  Make sure that you call parent::onBeforeDelete().", E_USER_ERROR);
		}
		
		// Deleting a record without an ID shouldn't do anything
		if(!$this->ID) throw new Exception("DataObject::delete() called on a DataObject without an ID");
		
		foreach($this->getClassAncestry() as $ancestor) {
			if(self::has_own_table($ancestor)) {
				$sql = new SQLQuery();
				$sql->delete = true;
				$sql->from[$ancestor] = "\"$ancestor\"";
				$sql->where[] = "\"ID\" = $this->ID";
				$this->extend('augmentSQL', $sql);
				$sql->execute();
			}
		}
		// Remove this item out of any caches
		$this->flushCache();
		
		$this->onAfterDelete();

		$this->OldID = $this->ID;
		$this->ID = 0;

		DataObjectLog::deletedObject($this);
	}

	/**
	 * Delete the record with the given ID.
	 *
	 * @param string $className The class name of the record to be deleted
	 * @param int $id ID of record to be deleted
	 */
	public static function delete_by_id($className, $id) {
		$obj = DataObject::get_by_id($className, $id);
		if($obj) {
			$obj->delete();
		} else {
			user_error("$className object #$id wasn't found when calling DataObject::delete_by_id", E_USER_WARNING);
		}
	}

	/**
	 * A cache used by getClassAncestry()
	 * @var array
	 */
	protected static $ancestry;

	/**
	 * Get the class ancestry, including the current class name.
	 * The ancestry will be returned as an array of class names, where the 0th element
	 * will be the class that inherits directly from DataObject, and the last element
	 * will be the current class.
	 *
	 * @return array Class ancestry
	 */
	public function getClassAncestry() {
		if(!isset(DataObject::$ancestry[$this->class])) {
			DataObject::$ancestry[$this->class] = array($this->class);
			while(($class = get_parent_class(DataObject::$ancestry[$this->class][0])) != "DataObject") {
				array_unshift(DataObject::$ancestry[$this->class], $class);
			}
		}
		return DataObject::$ancestry[$this->class];
	}

	/**
	 * Return a component object from a one to one relationship, as a DataObject.
	 * If no component is available, an 'empty component' will be returned.
	 *
	 * @param string $componentName Name of the component
	 *
	 * @return DataObject The component object. It's exact type will be that of the component.
	 */
	public function getComponent($componentName) {
		if(isset($this->components[$componentName])) {
			return $this->components[$componentName];
		}
		
		if($class = $this->has_one($componentName)) {
			$joinField = $componentName . 'ID';
			$joinID    = $this->getField($joinField);
			
			if($joinID) {
				$component = DataObject::get_by_id($class, $joinID);
			}
			
			if(!isset($component) || !$component) {
				$component = new $class();
			}
		} elseif($class = $this->belongs_to($componentName)) {
			$joinField = $this->getRemoteJoinField($componentName, 'belongs_to');
			$joinID    = $this->ID;
			
			if($joinID) {
				$component = DataObject::get_one($class, "\"$joinField\" = $joinID");
			}
			
			if(!isset($component) || !$component) {
				$component = new $class();
				$component->$joinField = $this->ID;
			}
		} else {
			throw new Exception("DataObject->getComponent(): Could not find component '$componentName'.");
		}
		
		$this->components[$componentName] = $component;
		return $component;
	}

	/**
	 * A cache used by component getting classes
	 * @var array
	 */
	protected $componentCache;

	/**
	 * Returns a one-to-many component, as a ComponentSet.
	 * The return value will be cached on this object instance,
	 * but only when no related objects are found (to avoid unnecessary empty checks in the database).
	 * If related objects exist, no caching is applied.
	 *
	 * @param string $componentName Name of the component
	 * @param string $filter A filter to be inserted into the WHERE clause
	 * @param string|array $sort A sort expression to be inserted into the ORDER BY clause. If omitted, the static field $default_sort on the component class will be used.
	 * @param string $join A single join clause. This can be used for filtering, only 1 instance of each DataObject will be returned.
	 * @param string|array $limit A limit expression to be inserted into the LIMIT clause
	 *
	 * @return ComponentSet The components of the one-to-many relationship.
	 */
	public function getComponents($componentName, $filter = "", $sort = "", $join = "", $limit = "") {
		$result = null;

		$sum = md5("{$filter}_{$sort}_{$join}_{$limit}");
		if(isset($this->componentCache[$componentName . '_' . $sum]) && false != $this->componentCache[$componentName . '_' . $sum]) {
			return $this->componentCache[$componentName . '_' . $sum];
		}

		if(!$componentClass = $this->has_many($componentName)) {
			user_error("DataObject::getComponents(): Unknown 1-to-many component '$componentName' on class '$this->class'", E_USER_ERROR);
		}

		$joinField = $this->getRemoteJoinField($componentName, 'has_many');

		if($this->isInDB()) { //Check to see whether we should query the db
			$query = $this->getComponentsQuery($componentName, $filter, $sort, $join, $limit);
			$result = $this->buildDataObjectSet($query->execute(), 'ComponentSet', $query, $componentClass);
			if($result) $result->parseQueryLimit($query);
		}

		if(!$result) {
			// If this record isn't in the database, then we want to hold onto this specific ComponentSet,
			// because it's the only copy of the data that we have.
			$result = new ComponentSet();
			$this->setComponent($componentName . '_' . $sum, $result);
		}

		$result->setComponentInfo("1-to-many", $this, null, null, $componentClass, $joinField);

		return $result;
	}

	/**
	 * Get the query object for a $has_many Component.
	 *
	 * Use {@link DataObjectSet->setComponentInfo()} to attach metadata to the
	 * resultset you're building with this query.
	 * Use {@link DataObject->buildDataObjectSet()} to build a set out of the {@link SQLQuery}
	 * object, and pass "ComponentSet" as a $containerClass.
	 *
	 * @param string $componentName
	 * @param string $filter
	 * @param string|array $sort
	 * @param string $join
	 * @param string|array $limit
	 * @return SQLQuery
	 */
	public function getComponentsQuery($componentName, $filter = "", $sort = "", $join = "", $limit = "") {
		if(!$componentClass = $this->has_many($componentName)) {
			user_error("DataObject::getComponentsQuery(): Unknown 1-to-many component '$componentName' on class '$this->class'", E_USER_ERROR);
		}

		$joinField = $this->getRemoteJoinField($componentName, 'has_many');

		$id = $this->getField("ID");
			
		// get filter
		$combinedFilter = "\"$joinField\" = '$id'";
		if($filter) $combinedFilter .= " AND {$filter}";
			
		return singleton($componentClass)->extendedSQL($combinedFilter, $sort, $limit, $join);
	}
	
	/**
	 * Tries to find the database key on another object that is used to store a relationship to this class. If no join
	 * field can be found it defaults to 'ParentID'.
	 *
	 * @param string $component
	 * @param string $type the join type - either 'has_many' or 'belongs_to'
	 * @return string
	 */
	public function getRemoteJoinField($component, $type = 'has_many') {
		$remoteClass = $this->$type($component, false);
		
		if(!$remoteClass) {
			throw new Exception("Unknown $type component '$component' on class '$this->class'");
		}
		
		if($fieldPos = strpos($remoteClass, '.')) {
			return substr($remoteClass, $fieldPos + 1) . 'ID';
		}
		
		$remoteRelations = array_flip(Object::combined_static($remoteClass, 'has_one', 'DataObject'));
		
		// look for remote has_one joins on this class or any parent classes
		foreach(array_reverse(ClassInfo::ancestry($this)) as $class) {
			if(array_key_exists($class, $remoteRelations)) return $remoteRelations[$class] . 'ID';
		}
		
		return 'ParentID';
	}
	
	/**
	 * Sets the component of a relationship.
	 * This should only need to be called internally,
	 * and is mainly due to the caching logic in {@link getComponents()}
	 * and {@link getManyManyComponents()}.
	 *
	 * @param string $componentName Name of the component
	 * @param DataObject|ComponentSet $componentValue Value of the component
	 */
	public function setComponent($componentName, $componentValue) {
		$this->componentCache[$componentName] = $componentValue;
	}

	/**
	 * Returns a many-to-many component, as a ComponentSet.
	 * The return value will be cached on this object instance,
	 * but only when no related objects are found (to avoid unnecessary empty checks in the database).
	 * If related objects exist, no caching is applied.
	 * 
	 * @param string $componentName Name of the many-many component
	 * @return ComponentSet The set of components
	 *
	 * @todo Implement query-params
	 */
	public function getManyManyComponents($componentName, $filter = "", $sort = "", $join = "", $limit = "") {
		$sum = md5("{$filter}_{$sort}_{$join}_{$limit}");
		if(isset($this->componentCache[$componentName . '_' . $sum]) && false != $this->componentCache[$componentName . '_' . $sum]) {
			return $this->componentCache[$componentName . '_' . $sum];
		}

		list($parentClass, $componentClass, $parentField, $componentField, $table) = $this->many_many($componentName);

		// Join expression is done on SiteTree.ID even if we link to Page; it helps work around
		// database inconsistencies
		$componentBaseClass = ClassInfo::baseDataClass($componentClass);

		if($this->ID && is_numeric($this->ID)) {
				
			if($componentClass) {
				$query = $this->getManyManyComponentsQuery($componentName, $filter, $sort, $join, $limit);
				$records = $query->execute();
				$result = $this->buildDataObjectSet($records, "ComponentSet", $query, $componentBaseClass);
				if($result) $result->parseQueryLimit($query); // for pagination support
				if(!$result) {
					$result = new ComponentSet();
				}
			}
		} else {
			$result = new ComponentSet();
		}
		$result->setComponentInfo("many-to-many", $this, $parentClass, $table, $componentClass);

		// If this record isn't in the database, then we want to hold onto this specific ComponentSet,
		// because it's the only copy of the data that we have.
		if(!$this->isInDB()) {
			$this->setComponent($componentName . '_' . $sum, $result);
		}

		return $result;
	}

	/**
	 * Get the query object for a $many_many Component.
	 * Use {@link DataObjectSet->setComponentInfo()} to attach metadata to the
	 * resultset you're building with this query.
	 * Use {@link DataObject->buildDataObjectSet()} to build a set out of the {@link SQLQuery}
	 * object, and pass "ComponentSet" as a $containerClass.
	 *
	 * @param string $componentName
	 * @param string $filter
	 * @param string|array $sort
	 * @param string $join
	 * @param string|array $limit
	 * @return SQLQuery
	 */
	public function getManyManyComponentsQuery($componentName, $filter = "", $sort = "", $join = "", $limit = "") {
		list($parentClass, $componentClass, $parentField, $componentField, $table) = $this->many_many($componentName);

		$componentObj = singleton($componentClass);

		// Join expression is done on SiteTree.ID even if we link to Page; it helps work around
		// database inconsistencies
		$componentBaseClass = ClassInfo::baseDataClass($componentClass);


		$query = $componentObj->extendedSQL(
			"\"$table\".\"$parentField\" = $this->ID", // filter 
			$sort,
			$limit,
			"INNER JOIN \"$table\" ON \"$table\".\"$componentField\" = \"$componentBaseClass\".\"ID\"" // join
		);
		
		foreach((array)$this->many_many_extraFields($componentName) as $extraField => $extraFieldType) {
			$query->select[] = "\"$table\".\"$extraField\"";
			$query->groupby[] = "\"$table\".\"$extraField\"";
		}

		if($filter) $query->where[] = $filter;
		if($join) $query->from[] = $join;

		return $query;
	}

	/**
	 * Pull out a join clause for a many-many relationship.
	 *
	 * @param string $componentName The many_many or belongs_many_many relation to join to.
	 * @param string $baseTable The classtable that will already be included in the SQL query to which this join will be added.
	 * @return string SQL join clause
	 */
	function getManyManyJoin($componentName, $baseTable) {
		if(!$componentClass = $this->many_many($componentName)) {
			user_error("DataObject::getComponents(): Unknown many-to-many component '$componentName' on class '$this->class'", E_USER_ERROR);
		}
		$classes = array_reverse(ClassInfo::ancestry($this->class));

		list($parentClass, $componentClass, $parentField, $componentField, $table) = $this->many_many($componentName);

		$baseComponentClass = ClassInfo::baseDataClass($componentClass);
		if($baseTable == $parentClass) {
			return "LEFT JOIN \"$table\" ON (\"$table\".\"$parentField\" = \"$parentClass\".\"ID\" AND \"$table\".\"$componentField\" = '{$this->ID}')";
		} else {
			return "LEFT JOIN \"$table\" ON (\"$table\".\"$componentField\" = \"$baseComponentClass\".\"ID\" AND \"$table\".\"$parentField\" = '{$this->ID}')";
		}
	}

	function getManyManyFilter($componentName, $baseTable) {
		list($parentClass, $componentClass, $parentField, $componentField, $table) = $this->many_many($componentName);

		return "\"$table\".\"$parentField\" = '{$this->ID}'";
	}

	/**
	 * Return an aggregate object. An aggregate object returns the result of running some SQL aggregate function on a field of 
	 * this dataobject type.
	 * 
	 * It can be called with no arguments, in which case it returns an object that calculates aggregates on this object's type,
	 * or with an argument (possibly statically), in which case it returns an object for that type
	 */
	function Aggregate($type = null, $filter = '') {
		return new Aggregate($type ? $type : $this->class, $filter);
	}
	
	/**
	 * Return an relationship aggregate object. A relationship aggregate does the same thing as an aggregate object, but operates
	 * on a has_many rather than directly on the type specified
	 */
	function RelationshipAggregate($object = null, $relationship = '', $filter = '') {
		if (is_string($object)) { $filter = $relationship; $relationship = $object; $object = $this; }
		return new Aggregate_Relationship($object ? $object : $this->owner, $relationship, $filter);
	}
	
	/**
	 * Return the class of a one-to-one component.  If $component is null, return all of the one-to-one components and their classes.
	 *
	 * @param string $component Name of component
	 *
	 * @return string|array The class of the one-to-one component, or an array of all one-to-one components and their classes.
	 */
	public function has_one($component = null) {
		$classes = ClassInfo::ancestry($this);

		foreach($classes as $class) {
			// Wait until after we reach DataObject
			if(in_array($class, array('Object', 'ViewableData', 'DataObject'))) continue;

			if($component) {
				$hasOne = Object::uninherited_static($class, 'has_one');
				
				if(isset($hasOne[$component])) {
					return $hasOne[$component];
				}
			} else {
				$newItems = (array) Object::uninherited_static($class, 'has_one');
				// Validate the data
				foreach($newItems as $k => $v) {
					if(!is_string($k) || is_numeric($k) || !is_string($v)) user_error("$class::\$has_one has a bad entry: " 
						. var_export($k,true). " => " . var_export($v,true) . ".  Each map key should be a relationship name, and the map value should be the data class to join to.", E_USER_ERROR);
				}
				$items = isset($items) ? array_merge($newItems, (array)$items) : $newItems;
			}
		}
		return isset($items) ? $items : null;
	}
	
	/**
	 * Returns the class of a remote belongs_to relationship. If no component is specified a map of all components and
	 * their class name will be returned.
	 *
	 * @param string $component
	 * @param bool $classOnly If this is TRUE, than any has_many relationships in the form "ClassName.Field" will have
	 *        the field data stripped off. It defaults to TRUE.
	 * @return string|array
	 */
	public function belongs_to($component = null, $classOnly = true) {
		$belongsTo = Object::combined_static($this->class, 'belongs_to', 'DataObject');
		
		if($component) {
			if($belongsTo && array_key_exists($component, $belongsTo)) {
				$belongsTo = $belongsTo[$component];
			} else {
				return false;
			}
		}
		
		if($belongsTo && $classOnly) {
			return preg_replace('/(.+)?\..+/', '$1', $belongsTo);
		} else {
			return $belongsTo ? $belongsTo : array();
		}
	}
	
	/**
	 * Return all of the database fields defined in self::$db and all the parent classes.
	 * Doesn't include any fields specified by self::$has_one.  Use $this->has_one() to get these fields
	 *
	 * @param string $fieldName Limit the output to a specific field name
	 * @return array The database fields
	 */
	public function db($fieldName = null) {
		$classes = ClassInfo::ancestry($this);
		$good = false;
		$items = array();
		
		foreach($classes as $class) {
			// Wait until after we reach DataObject
			if(!$good) {
				if($class == 'DataObject') {
					$good = true;
				}
				continue;
			}

			if($fieldName) {
				$db = Object::uninherited_static($class, 'db');
				
				if(isset($db[$fieldName])) {
					return $db[$fieldName];
				}
			} else {
				$newItems = (array) Object::uninherited_static($class, 'db');
				// Validate the data
				foreach($newItems as $k => $v) {
					if(!is_string($k) || is_numeric($k) || !is_string($v)) user_error("$class::\$db has a bad entry: " 
						. var_export($k,true). " => " . var_export($v,true) . ".  Each map key should be a property name, and the map value should be the property type.", E_USER_ERROR);
				}
				$items = isset($items) ? array_merge((array)$items, $newItems) : $newItems;
			}
		}

		return $items;
	}

	/**
	 * Gets the class of a one-to-many relationship. If no $component is specified then an array of all the one-to-many
	 * relationships and their classes will be returned.
	 *
	 * @param string $component Name of component
	 * @param bool $classOnly If this is TRUE, than any has_many relationships in the form "ClassName.Field" will have
	 *        the field data stripped off. It defaults to TRUE.
	 * @return string|array
	 */
	public function has_many($component = null, $classOnly = true) {
		$hasMany = Object::combined_static($this->class, 'has_many', 'DataObject');
		
		if($component) {
			if($hasMany && array_key_exists($component, $hasMany)) {
				$hasMany = $hasMany[$component];
			} else {
				return false;
			}
		}
		
		if($hasMany && $classOnly) {
			return preg_replace('/(.+)?\..+/', '$1', $hasMany);
		} else {
			return $hasMany ? $hasMany : array();
		}
	}

	/**
	 * Return the many-to-many extra fields specification.
	 * 
	 * If you don't specify a component name, it returns all
	 * extra fields for all components available.
	 * 
	 * @param string $component Name of component
	 * @return array
	 */
	public function many_many_extraFields($component = null) {
		$classes = ClassInfo::ancestry($this);

		foreach($classes as $class) {
			if(in_array($class, array('ViewableData', 'Object', 'DataObject'))) continue;
			$relationName = null;

			// Find extra fields for one component
			if($component) {
				$SNG_class = singleton($class);
				$extraFields = $SNG_class->stat('many_many_extraFields');

				// Extra fields are immediately available on this class
				if(isset($extraFields[$component])) {
					return $extraFields[$component];
				}
				
				$manyMany = $SNG_class->stat('many_many');
				$candidate = (isset($manyMany[$component])) ? $manyMany[$component] : null;
				if($candidate) {
					$SNG_candidate = singleton($candidate);
					$candidateManyMany = $SNG_candidate->stat('belongs_many_many');
					
					// Find the relation given the class
					if($candidateManyMany) foreach($candidateManyMany as $relation => $relatedClass) {
						if($relatedClass == $class) {
							$relationName = $relation;
							break;
						}
					}
					
					if($relationName) {
						$extraFields = $SNG_candidate->stat('many_many_extraFields');
						if(isset($extraFields[$relationName])) {
							return $extraFields[$relationName];
						}
					}
				}
								
				$manyMany = $SNG_class->stat('belongs_many_many');
				$candidate = (isset($manyMany[$component])) ? $manyMany[$component] : null;
				if($candidate) {
					$SNG_candidate = singleton($candidate);
					$candidateManyMany = $SNG_candidate->stat('many_many');
					
					// Find the relation given the class
					if($candidateManyMany) foreach($candidateManyMany as $relation => $relatedClass) {
						if($relatedClass == $class) {
							$relationName = $relation;
						}
					}
					
					$extraFields = $SNG_candidate->stat('many_many_extraFields');
					if(isset($extraFields[$relationName])) {
						return $extraFields[$relationName];
					}
				}
				
			} else {
				
				// Find all the extra fields for all components
				$newItems = eval("return (array){$class}::\$many_many_extraFields;");
				
				foreach($newItems as $k => $v) {
					if(!is_array($v)) {
						user_error(
							"$class::\$many_many_extraFields has a bad entry: "
							. var_export($k, true) . " => " . var_export($v, true)
							. ". Each many_many_extraFields entry should map to a field specification array.",
							E_USER_ERROR
						);
					}
				}
					
				return isset($items) ? array_merge($newItems, $items) : $newItems;
			}
		}
	}
	
	/**
	 * Return information about a many-to-many component.
	 * The return value is an array of (parentclass, childclass).  If $component is null, then all many-many
	 * components are returned.
	 *
	 * @param string $component Name of component
	 *
	 * @return array  An array of (parentclass, childclass), or an array of all many-many components
	 */
	public function many_many($component = null) {
		$classes = ClassInfo::ancestry($this);

		foreach($classes as $class) {
			// Wait until after we reach DataObject
			if(in_array($class, array('ViewableData', 'Object', 'DataObject'))) continue;

			if($component) {
				$manyMany = Object::uninherited_static($class, 'many_many');
				// Try many_many
				$candidate = (isset($manyMany[$component])) ? $manyMany[$component] : null;
				if($candidate) {
					$parentField = $class . "ID";
					$childField = ($class == $candidate) ? "ChildID" : $candidate . "ID";
					return array($class, $candidate, $parentField, $childField, "{$class}_$component");
				}

				// Try belongs_many_many
				$belongsManyMany = Object::uninherited_static($class, 'belongs_many_many');
				$candidate = (isset($belongsManyMany[$component])) ? $belongsManyMany[$component] : null;
				if($candidate) {
					$childField = $candidate . "ID";

					// We need to find the inverse component name
					$otherManyMany = Object::uninherited_static($candidate, 'many_many');
					if(!$otherManyMany) {
						user_error("Inverse component of $candidate not found ({$this->class})", E_USER_ERROR);
					}

					foreach($otherManyMany as $inverseComponentName => $candidateClass) {
						if($candidateClass == $class || is_subclass_of($class, $candidateClass)) {
							$parentField = ($class == $candidate) ? "ChildID" : $candidateClass . "ID";
							// HACK HACK HACK!
							if($component == 'NestedProducts') {
								$parentField = $candidateClass . "ID";
							}

							return array($class, $candidate, $parentField, $childField, "{$candidate}_$inverseComponentName");
						}
					}
					user_error("Orphaned \$belongs_many_many value for $this->class.$component", E_USER_ERROR);
				}
			} else {
				$newItems = (array) Object::uninherited_static($class, 'many_many');
				// Validate the data
				foreach($newItems as $k => $v) {
					if(!is_string($k) || is_numeric($k) || !is_string($v)) user_error("$class::\$many_many has a bad entry: " 
						. var_export($k,true). " => " . var_export($v,true) . ".  Each map key should be a relationship name, and the map value should be the data class to join to.", E_USER_ERROR);
				}
				$items = isset($items) ? array_merge($newItems, $items) : $newItems;
				
				$newItems = (array) Object::uninherited_static($class, 'belongs_many_many');
				// Validate the data
				foreach($newItems as $k => $v) {
					if(!is_string($k) || is_numeric($k) || !is_string($v)) user_error("$class::\$belongs_many_many has a bad entry: " 
						. var_export($k,true). " => " . var_export($v,true) . ".  Each map key should be a relationship name, and the map value should be the data class to join to.", E_USER_ERROR);
				}

				$items = isset($items) ? array_merge($newItems, $items) : $newItems;
			}
		}
		
		return isset($items) ? $items : null;
	}
	
	/**
	 * This returns an array (if it exists) describing the database extensions that are required, or false if none
	 * 
	 * This is experimental, and is currently only a Postgres-specific enhancement.
	 * 
	 * @return array or false
	 */
	function database_extensions($class){
		
		$extensions = Object::uninherited_static($class, 'database_extensions');
		
		if($extensions)
			return $extensions;
		else
			return false;
	}

	/**
	 * Generates a SearchContext to be used for building and processing
	 * a generic search form for properties on this object.
	 *
	 * @return SearchContext
	 */
	public function getDefaultSearchContext() {
		return new SearchContext(
			$this->class, 
			$this->scaffoldSearchFields(), 
			$this->defaultSearchFilters()
		);
	}
	
	/**
	 * Determine which properties on the DataObject are
	 * searchable, and map them to their default {@link FormField}
	 * representations. Used for scaffolding a searchform for {@link ModelAdmin}.
	 *
	 * Some additional logic is included for switching field labels, based on
	 * how generic or specific the field type is.
	 *
	 * Used by {@link SearchContext}.
	 * 
	 * @param array $_params
	 * 	'fieldClasses': Associative array of field names as keys and FormField classes as values
	 * 	'restrictFields': Numeric array of a field name whitelist
	 * @return FieldSet
	 */
	public function scaffoldSearchFields($_params = null) {
		$params = array_merge(
			array(
				'fieldClasses' => false,
				'restrictFields' => false
			),
			(array)$_params
		);
		$fields = new FieldSet();
		foreach($this->searchableFields() as $fieldName => $spec) {
			if($params['restrictFields'] && !in_array($fieldName, $params['restrictFields'])) continue;
			
			// If a custom fieldclass is provided as a string, use it
			if($params['fieldClasses'] && isset($params['fieldClasses'][$fieldName])) {
				$fieldClass = $params['fieldClasses'][$fieldName];
				$field = new $fieldClass($fieldName);
			// If we explicitly set a field, then construct that
			} else if(isset($spec['field'])) {
				// If it's a string, use it as a class name and construct
				if(is_string($spec['field'])) {
					$fieldClass = $spec['field'];
					$field = new $fieldClass($fieldName);
					
				// If it's a FormField object, then just use that object directly.
				} else if($spec['field'] instanceof FormField) {
					$field = $spec['field'];
					
				// Otherwise we have a bug
				} else {
					user_error("Bad value for searchable_fields, 'field' value: " . var_export($spec['field'], true), E_USER_WARNING);
				}
				
			// Otherwise, use the database field's scaffolder
			} else {
				$field = $this->relObject($fieldName)->scaffoldSearchField();
			}

			if (strstr($fieldName, '.')) {
				$field->setName(str_replace('.', '__', $fieldName));
			}
			$field->setTitle($spec['title']);

			$fields->push($field);
		}
		return $fields;
	}

	/**
	 * Scaffold a simple edit form for all properties on this dataobject,
	 * based on default {@link FormField} mapping in {@link DBField::scaffoldFormField()}.
	 * Field labels/titles will be auto generated from {@link DataObject::fieldLabels()}.
	 *
	 * @uses FormScaffolder
	 * 
	 * @param array $_params Associative array passing through properties to {@link FormScaffolder}.
	 * @return FieldSet
	 */
	public function scaffoldFormFields($_params = null) {
		$params = array_merge(
			array(
				'tabbed' => false,
				'includeRelations' => false,
				'restrictFields' => false,
				'fieldClasses' => false,
				'ajaxSafe' => false
			),
			(array)$_params
		);
		
		$fs = new FormScaffolder($this);
		$fs->tabbed = $params['tabbed'];
		$fs->includeRelations = $params['includeRelations'];
		$fs->restrictFields = $params['restrictFields'];
		$fs->fieldClasses = $params['fieldClasses'];
		$fs->ajaxSafe = $params['ajaxSafe'];
		
		return $fs->getFieldSet();
	}
	
	/**
	 * Centerpiece of every data administration interface in Silverstripe,
	 * which returns a {@link FieldSet} suitable for a {@link Form} object.
	 * If not overloaded, we're using {@link scaffoldFormFields()} to automatically
	 * generate this set. To customize, overload this method in a subclass
	 * or decorate onto it by using {@link DataObjectDecorator->updateCMSFields()}.
	 *
	 * <code>
	 * klass MyCustomClass extends DataObject {
	 * 	static $db = array('CustomProperty'=>'Boolean');
	 *
	 * 	public function getCMSFields() {
	 * 		$fields = parent::getCMSFields();
	 * 		$fields->addFieldToTab('Root.Content',new CheckboxField('CustomProperty'));
	 *		return $fields;
	 *	}
	 * }
	 * </code>
	 *
	 * @see Good example of complex FormField building: SiteTree::getCMSFields()
	 *
	 * @param array $params See {@link scaffoldFormFields()}
	 * @return FieldSet Returns a TabSet for usage within the CMS - don't use for frontend forms.
	 */
	public function getCMSFields($params = null) {
		$tabbedFields = $this->scaffoldFormFields(array_merge(
			array(
				'includeRelations' => true,
				'tabbed' => true,
				'ajaxSafe' => true
			),
			(array)$params
		));
		
		$this->extend('updateCMSFields', $tabbedFields);
		
		return $tabbedFields;
	}
	
	/**
	 * need to be overload by solid dataobject, so that the customised actions of that dataobject,
	 * including that dataobject's decorator customised actions could be added to the EditForm.
	 * 
	 * @return an Empty FieldSet(); need to be overload by solid subclass
	 */
	public function getCMSActions() {
		$actions = new FieldSet();
		$this->extend('updateCMSActions', $actions);
		return $actions;
	}
	

	/**
	 * Used for simple frontend forms without relation editing
	 * or {@link TabSet} behaviour. Uses {@link scaffoldFormFields()}
	 * by default. To customize, either overload this method in your
	 * subclass, or decorate it by {@link DataObjectDecorator->updateFrontEndFields()}.
	 * 
	 * @todo Decide on naming for "website|frontend|site|page" and stick with it in the API
	 *
	 * @param array $params See {@link scaffoldFormFields()}
	 * @return FieldSet Always returns a simple field collection without TabSet.
	 */
	public function getFrontEndFields($params = null) {
		$untabbedFields = $this->scaffoldFormFields($params);
		$this->extend('updateFrontEndFields', $untabbedFields);
	
		return $untabbedFields;
	}

	/**
	 * Gets the value of a field.
	 * Called by {@link __get()} and any getFieldName() methods you might create.
	 *
	 * @param string $field The name of the field
	 *
	 * @return mixed The field value
	 */
	public function getField($field) {
		// If we already have an object in $this->record, then we should just return that
		if(isset($this->record[$field]) && is_object($this->record[$field]))  return $this->record[$field];
		
		// Otherwise, we need to determine if this is a complex field
		if(self::is_composite_field($this->class, $field)) {
			$helper = $this->castingHelper($field);
			$fieldObj = Object::create_from_string($helper, $field);
			
			// write value only if either the field value exists,
			// or a valid record has been loaded from the database
			$value = (isset($this->record[$field])) ? $this->record[$field] : null;
			if($value || $this->exists()) $fieldObj->setValue($value, $this->record, false);
			
			$this->record[$field] = $fieldObj;

			return $this->record[$field];
		}

		return isset($this->record[$field]) ? $this->record[$field] : null;
	}

	/**
	 * Return a map of all the fields for this record.
	 *
	 * @return array A map of field names to field values.
	 */
	public function getAllFields() {
		return $this->record;
	}

	/**
	 * Return the fields that have changed.
	 * 
	 * The change level affects what the functions defines as "changed":
	 * - Level 1 will return strict changes, even !== ones.
	 * - Level 2 is more lenient, it will only return real data changes, for example a change from 0 to null
	 * would not be included.
	 *
	 * Example return:
	 * <code>
	 * array(
	 *   'Title' = array('before' => 'Home', 'after' => 'Home-Changed', 'level' => 2)
	 * )
	 * </code>
	 *
	 * @param boolean $databaseFieldsOnly Get only database fields that have changed
	 * @param int $changeLevel The strictness of what is defined as change
	 * @return array
	 */
	public function getChangedFields($databaseFieldsOnly = false, $changeLevel = 1) {
		$changedFields = array();
		
		// Update the changed array with references to changed obj-fields
		foreach($this->record as $k => $v) {
			if(is_object($v) && method_exists($v, 'isChanged') && $v->isChanged()) {
				$this->changed[$k] = 1;
			}
		}
		
		if($databaseFieldsOnly) {
			$databaseFields = $this->inheritedDatabaseFields();
			$databaseFields['ID'] = true;
			$databaseFields['LastEdited'] = true;
			$databaseFields['Created'] = true;
			$databaseFields['ClassName'] = true;
			$fields = array_intersect_key((array)$this->changed, $databaseFields);
		} else {
			$fields = $this->changed;
		}

		// Filter the list to those of a certain change level
		if($changeLevel > 1) {
			if($fields) foreach($fields as $name => $level) {
				if($level < $changeLevel) {
					unset($fields[$name]);
				}
			}
		}
		
		if($fields) foreach($fields as $name => $level) {
			$changedFields[$name] = array(
				'before' => array_key_exists($name, $this->original) ? $this->original[$name] : null,
				'after' => array_key_exists($name, $this->record) ? $this->record[$name] : null,
				'level' => $level
			);
		}

		return $changedFields;
	}
	
	/**
	 * Uses {@link getChangedFields()} to determine if fields have been changed
	 * since loading them from the database.
	 * 
	 * @param string $fieldName Name of the database field to check, will check for any if not given
	 * @param int $changeLevel See {@link getChangedFields()}
	 * @return boolean
	 */
	function isChanged($fieldName = null, $changeLevel = 1) {
		$changed = $this->getChangedFields(false, $changeLevel);
		if(!isset($fieldName)) {
			return !empty($changed);
		} 
		else {
			return array_key_exists($fieldName, $changed);
		}
	}

	/**
	 * Set the value of the field
	 * Called by {@link __set()} and any setFieldName() methods you might create.
	 *
	 * @param string $fieldName Name of the field
	 * @param mixed $val New field value
	 */
	function setField($fieldName, $val) {
		// Situation 1: Passing an DBField
		if($val instanceof DBField) {
			$val->Name = $fieldName;
			$this->record[$fieldName] = $val;
		// Situation 2: Passing a literal or non-DBField object
		} else {
			// If this is a proper database field, we shouldn't be getting non-DBField objects
			if(is_object($val) && $this->db($fieldName)) {
				user_error('DataObject::setField: passed an object that is not a DBField', E_USER_WARNING);
			}
		
			$defaults = $this->stat('defaults');
			// if a field is not existing or has strictly changed
			if(!isset($this->record[$fieldName]) || $this->record[$fieldName] !== $val) {
				// TODO Add check for php-level defaults which are not set in the db
				// TODO Add check for hidden input-fields (readonly) which are not set in the db
				// At the very least, the type has changed
				$this->changed[$fieldName] = 1;
				
				if((!isset($this->record[$fieldName]) && $val) || (isset($this->record[$fieldName]) && $this->record[$fieldName] != $val)) {
					// Value has changed as well, not just the type
					$this->changed[$fieldName] = 2;
				}

				// value is always saved back when strict check succeeds
				$this->record[$fieldName] = $val;
			}
		}
	}

	/**
	 * Set the value of the field, using a casting object.
	 * This is useful when you aren't sure that a date is in SQL format, for example.
	 * setCastedField() can also be used, by forms, to set related data.  For example, uploaded images
	 * can be saved into the Image table.
	 *
	 * @param string $fieldName Name of the field
	 * @param mixed $value New field value
	 */
	public function setCastedField($fieldName, $val) {
		if(!$fieldName) {
			user_error("DataObject::setCastedField: Called without a fieldName", E_USER_ERROR);
		}
		$castingHelper = $this->castingHelper($fieldName);
		if($castingHelper) {
			$fieldObj = Object::create_from_string($castingHelper, $fieldName);
			$fieldObj->setValue($val);
			$fieldObj->saveInto($this);
		} else {
			$this->$fieldName = $val;
		}
	}

	/**
	 * Returns true if the given field exists
	 * in a database column on any of the objects tables,
	 * or as a dynamic getter with get<fieldName>().
	 *
	 * @param string $field Name of the field
	 * @return boolean True if the given field exists
	 */
	public function hasField($field) {
		return (
			array_key_exists($field, $this->record) 
			|| $this->db($field)
			|| $this->hasMethod("get{$field}")
		);
	}

	/**
	 * Returns true if the given field exists as a database column
	 *
	 * @param string $field Name of the field
	 *
	 * @return boolean
	 */
	public function hasDatabaseField($field) {
		// Add base fields which are not defined in static $db
		static $fixedFields = array(
			'ID' => 'Int',
			'ClassName' => 'Enum',
			'LastEdited' => 'SS_Datetime',
			'Created' => 'SS_Datetime',
		);
		
		if(isset($fixedFields[$field])) return true;

		return array_key_exists($field, $this->inheritedDatabaseFields());
	}
	
	/**
	 * Returns the field type of the given field, if it belongs to this class, and not a parent.
	 * Note that the field type will not include constructor arguments in round brackets, only the classname.
	 *
	 * @param string $field Name of the field
	 * @return string The field type of the given field
	 */
	public function hasOwnTableDatabaseField($field) {
		// Add base fields which are not defined in static $db
		if($field == "ID") return "Int";
		if($field == "ClassName" && get_parent_class($this) == "DataObject") return "Enum";
		if($field == "LastEdited" && get_parent_class($this) == "DataObject") return "SS_Datetime";
		if($field == "Created" && get_parent_class($this) == "DataObject") return "SS_Datetime";

		// Add fields from Versioned decorator
		if($field == 'Version' && $this->hasExtension('Versioned')) { 
			return 'Int';
		}
		// get cached fieldmap
		$fieldMap = isset(self::$cache_has_own_table_field[$this->class]) ? self::$cache_has_own_table_field[$this->class] : null;
		
		// if no fieldmap is cached, get all fields
		if(!$fieldMap) {
			$fieldMap = Object::uninherited_static($this->class, 'db');
			
			// all $db fields on this specific class (no parents)
			foreach(self::composite_fields($this->class, false) as $fieldname => $fieldtype) {
				$combined_db = singleton($fieldtype)->compositeDatabaseFields();
				foreach($combined_db as $name => $type){
					$fieldMap[$fieldname.$name] = $type;
				}
			}
			
			// all has_one relations on this specific class,
			// add foreign key
			$hasOne = Object::uninherited_static($this->class, 'has_one');
			if($hasOne) foreach($hasOne as $fieldName => $fieldSchema) {
				$fieldMap[$fieldName . 'ID'] = "ForeignKey";
			}

			// set cached fieldmap
			self::$cache_has_own_table_field[$this->class] = $fieldMap;
		}

		// Remove string-based "constructor-arguments" from the DBField definition
		if(isset($fieldMap[$field])) {
			if(is_string($fieldMap[$field])) return strtok($fieldMap[$field],'(');
			else return $fieldMap[$field]['type'];
		}
	}
	
	/**
	 * Returns true if given class has its own table. Uses the rules for whether the table should exist rather than
	 * actually looking in the database.
	 *
	 * @param string $dataClass
	 * @return bool
	 */
	public static function has_own_table($dataClass) {
		
		// The condition below has the same effect as !is_subclass_of($dataClass,'DataObject'),
		// which causes PHP < 5.3 to segfault in rare circumstances, see PHP bug #46753
		if($dataClass == 'DataObject' || !in_array('DataObject', ClassInfo::ancestry($dataClass))) return false;
		
		if(!isset(self::$cache_has_own_table[$dataClass])) {
			if(get_parent_class($dataClass) == 'DataObject') {
				self::$cache_has_own_table[$dataClass] = true;
			} else {
				self::$cache_has_own_table[$dataClass] = Object::uninherited_static($dataClass, 'db') || Object::uninherited_static($dataClass, 'has_one');
			}
		}
		return self::$cache_has_own_table[$dataClass];
	}
	
	/**
	 * Returns true if the member is allowed to do the given action.
	 * See {@link extendedCan()} for a more versatile tri-state permission control.
	 *
	 * @param string $perm The permission to be checked, such as 'View'.
	 * @param Member $member The member whose permissions need checking.  Defaults to the currently logged
	 * in user.
	 *
	 * @return boolean True if the the member is allowed to do the given action
	 */
	function can($perm, $member = null) {
		if(!isset($member)) {
			$member = Member::currentUser();
		}
		if(Permission::checkMember($member, "ADMIN")) return true;

		if($this->many_many('Can' . $perm)) {
			if($this->ParentID && $this->SecurityType == 'Inherit') {
				if(!($p = $this->Parent)) {
					return false;
				}
				return $this->Parent->can($perm, $member);

			} else {
				$permissionCache = $this->uninherited('permissionCache');
				$memberID = $member ? $member->ID : 'none';

				if(!isset($permissionCache[$memberID][$perm])) {
					if($member->ID) {
						$groups = $member->Groups();
					}

					$groupList = implode(', ', $groups->column("ID"));

					$query = new SQLQuery(
						"\"Page_Can$perm\".PageID",
					array("\"Page_Can$perm\""),
						"GroupID IN ($groupList)");

					$permissionCache[$memberID][$perm] = $query->execute()->column();

					if($perm == "View") {
						$query = new SQLQuery("\"SiteTree\".\"ID\"", array(
							"\"SiteTree\"",
							"LEFT JOIN \"Page_CanView\" ON \"Page_CanView\".\"PageID\" = \"SiteTree\".\"ID\""
							), "\"Page_CanView\".\"PageID\" IS NULL");

							$unsecuredPages = $query->execute()->column();
							if($permissionCache[$memberID][$perm]) {
								$permissionCache[$memberID][$perm] = array_merge($permissionCache[$memberID][$perm], $unsecuredPages);
							} else {
								$permissionCache[$memberID][$perm] = $unsecuredPages;
							}
					}

					$this->set_uninherited('permissionCache', $permissionCache);
				}


				if($permissionCache[$memberID][$perm]) {
					return in_array($this->ID, $permissionCache[$memberID][$perm]);
				}
			}
		} else {
			return parent::can($perm, $member);
		}
	}

	/**
	 * Process tri-state responses from permission-alterting decorators.  The decorators are
	 * expected to return one of three values:
	 * 
	 *  - false: Disallow this permission, regardless of what other decorators say
	 *  - true: Allow this permission, as long as no other decorators return false
	 *  - NULL: Don't affect the outcome
	 * 
	 * This method itself returns a tri-state value, and is designed to be used like this:
	 *
	 * <code>
	 * $extended = $this->extendedCan('canDoSomething', $member);
	 * if($extended !== null) return $extended;
	 * else return $normalValue;
	 * </code>
	 * 
	 * @param String $methodName Method on the same object, e.g. {@link canEdit()}
	 * @param Member|int $member
	 * @return boolean|null
	 */
	public function extendedCan($methodName, $member) {
		$results = $this->extend($methodName, $member);
		if($results && is_array($results)) {
			// Remove NULLs
			$results = array_filter($results, array($this,'isNotNull'));
			// If there are any non-NULL responses, then return the lowest one of them.
			// If any explicitly deny the permission, then we don't get access 
			if($results) return min($results);
		}
		return null;
	}
	
	/**
	 * Helper functon for extendedCan
	 * 
	 * @param Mixed $value
	 * @return boolean
	 */
	private function isNotNull($value) {
		return !is_null($value);
	}

	/**
	 * @param Member $member
	 * @return boolean
	 */
	public function canView($member = null) {
		return Permission::check('ADMIN', 'any', $member);
	}

	/**
	 * @param Member $member
	 * @return boolean
	 */
	public function canEdit($member = null) {
		return Permission::check('ADMIN', 'any', $member);
	}

	/**
	 * @param Member $member
	 * @return boolean
	 */
	public function canDelete($member = null) {
		return Permission::check('ADMIN', 'any', $member);
	}

	/**
	 * @todo Should canCreate be a static method?
	 *
	 * @param Member $member
	 * @return boolean
	 */
	public function canCreate($member = null) {
		return Permission::check('ADMIN', 'any', $member);
	}

	/**
	 * Debugging used by Debug::show()
	 *
	 * @return string HTML data representing this object
	 */
	public function debug() {
		$val = "<h3>Database record: $this->class</h3>\n<ul>\n";
		if($this->record) foreach($this->record as $fieldName => $fieldVal) {
			$val .= "\t<li>$fieldName: " . Debug::text($fieldVal) . "</li>\n";
		}
		$val .= "</ul>\n";
		return $val;
	}

	/**
	 * Return the DBField object that represents the given field.
	 * This works similarly to obj() with 2 key differences:
	 *   - it still returns an object even when the field has no value.
	 *   - it only matches fields and not methods
	 *   - it matches foreign keys generated by has_one relationships, eg, "ParentID"
	 *
	 * @param string $fieldName Name of the field
	 * @return DBField The field as a DBField object
	 */
	public function dbObject($fieldName) {
		// If we have a CompositeDBField object in $this->record, then return that
		if(isset($this->record[$fieldName]) && is_object($this->record[$fieldName])) {
			return $this->record[$fieldName];
			
		// Special case for ID field
		} else if($fieldName == 'ID') {
			return new PrimaryKey($fieldName, $this);
			
		// General casting information for items in $db or $casting
		} else if($helper = $this->castingHelper($fieldName)) {
			$obj = Object::create_from_string($helper, $fieldName);
			$obj->setValue($this->$fieldName, $this->record, false);
			return $obj;
			
		// Special case for has_one relationships
		} else if(preg_match('/ID$/', $fieldName) && $this->has_one(substr($fieldName,0,-2))) {
			$val = (isset($this->record[$fieldName])) ? $this->record[$fieldName] : null;
			return DBField::create('ForeignKey', $val, $fieldName, $this);
			
		// Special case for ClassName
		} else if($fieldName == 'ClassName') {
			$val = get_class($this);
			return DBField::create('Varchar', $val, $fieldName, $this);
		}
	}

	/**
	 * Traverses to a DBField referenced by relationships between data objects.
	 * The path to the related field is specified with dot separated syntax (eg: Parent.Child.Child.FieldName)
	 *
	 * @param $fieldPath string
	 * @return DBField
	 */
	public function relObject($fieldPath) {
		$parts = explode('.', $fieldPath);
		$fieldName = array_pop($parts);
		$component = $this;
		foreach($parts as $relation) {
			if ($rel = $component->has_one($relation)) {
				$component = singleton($rel);
			} elseif ($rel = $component->has_many($relation)) {
				$component = singleton($rel);
			} elseif ($rel = $component->many_many($relation)) {
				$component = singleton($rel[1]);
			} elseif($className = $this->castingClass($relation)) {
				$component = $className;
			}
		}

		$object = $component->dbObject($fieldName);

		if (!($object instanceof DBField) && !($object instanceof ComponentSet)) {
			// Todo: come up with a broader range of exception objects to describe differnet kinds of errors programatically
			throw new Exception("Unable to traverse to related object field [$fieldPath] on [$this->class]");
		}
		return $object;
	}

	/**
	 * Temporary hack to return an association name, based on class, to get around the mangle
	 * of having to deal with reverse lookup of relationships to determine autogenerated foreign keys.
	 * 
	 * @return String
	 */
	public function getReverseAssociation($className) {
		if (is_array($this->many_many())) {
			$many_many = array_flip($this->many_many());
			if (array_key_exists($className, $many_many)) return $many_many[$className];
		}
		if (is_array($this->has_many())) {
			$has_many = array_flip($this->has_many());
			if (array_key_exists($className, $has_many)) return $has_many[$className];
		}
		if (is_array($this->has_one())) {
			$has_one = array_flip($this->has_one());
			if (array_key_exists($className, $has_one)) return $has_one[$className];
		}
		
		return false;
	}

	/**
	 * Build a {@link SQLQuery} object to perform the given query.
	 *
	 * @param string $filter A filter to be inserted into the WHERE clause.
	 * @param string|array $sort A sort expression to be inserted into the ORDER BY clause. If omitted, self::$default_sort will be used.
	 * @param string|array $limit A limit expression to be inserted into the LIMIT clause.
	 * @param string $join A single join clause. This can be used for filtering, only 1 instance of each DataObject will be returned.
	 * @param boolean $restictClasses Restrict results to only objects of either this class of a subclass of this class
	 * @param string $having A filter to be inserted into the HAVING clause.
	 *
	 * @return SQLQuery Query built.
	 */
	public function buildSQL($filter = "", $sort = "", $limit = "", $join = "", $restrictClasses = true, $having = "") {
		// Cache the big hairy part of buildSQL
		if(!isset(self::$cache_buildSQL_query[$this->class])) {
			// Get the tables to join to
			$tableClasses = ClassInfo::dataClassesFor($this->class);
			if(!$tableClasses) {
				if(!ManifestBuilder::has_been_included()) {
					user_error("DataObjects have been requested before the manifest is loaded. Please ensure you are not querying the database in _config.php.", E_USER_ERROR);
				} else {
					user_error("DataObject::buildSQL: Can't find data classes (classes linked to tables) for $this->class. Please ensure you run dev/build after creating a new DataObject.", E_USER_ERROR);
				}
			}

			$baseClass = array_shift($tableClasses);


			// $collidingFields will keep a list fields that appear in mulitple places in the class
			// heirarchy for this table.  They will be dealt with more explicitly in the SQL query
			// to ensure that junk data from other tables doesn't corrupt data objects
			$collidingFields = array();

			// Build our intial query
			$query = new SQLQuery(array());
			$query->from("\"$baseClass\"");

			// Add SQL for multi-value fields on the base table
			$databaseFields = self::database_fields($baseClass);
			if($databaseFields) foreach($databaseFields as $k => $v) {
				if(!in_array($k, array('ClassName', 'LastEdited', 'Created')) && ClassInfo::classImplements($v, 'CompositeDBField')) {
					$this->dbObject($k)->addToQuery($query);
				} else {
					$query->select[$k] = "\"$baseClass\".\"$k\"";
				}
			}
			// Join all the tables
			if($tableClasses && self::$subclass_access) {
				foreach($tableClasses as $tableClass) {
					$query->from[$tableClass] = "LEFT JOIN \"$tableClass\" ON \"$tableClass\".\"ID\" = \"$baseClass\".\"ID\"";

					// Add SQL for multi-value fields
					$databaseFields = self::database_fields($tableClass);
					$compositeFields = self::composite_fields($tableClass, false);
					if($databaseFields) foreach($databaseFields as $k => $v) {
						if(!isset($compositeFields[$k])) {
							// Update $collidingFields if necessary
							if(isset($query->select[$k])) {
								if(!isset($collidingFields[$k])) $collidingFields[$k] = array($query->select[$k]);
								$collidingFields[$k][] = "\"$tableClass\".\"$k\"";
								
							} else {
								$query->select[$k] = "\"$tableClass\".\"$k\"";
							}
						}
					}
					if($compositeFields) foreach($compositeFields as $k => $v) {
						$dbO = $this->dbObject($k);
						if($dbO) $dbO->addToQuery($query);
					}
				}
			}
			
			// Resolve colliding fields
			if($collidingFields) {
				foreach($collidingFields as $k => $collisions) {
					$caseClauses = array();
					foreach($collisions as $collision) {
						if(preg_match('/^"([^"]+)"/', $collision, $matches)) {
							$collisionBase = $matches[1];
							$collisionClasses = ClassInfo::subclassesFor($collisionBase);
							$caseClauses[] = "WHEN \"$baseClass\".\"ClassName\" IN ('"
								. implode("', '", $collisionClasses) . "') THEN $collision";
						} else {
							user_error("Bad collision item '$collision'", E_USER_WARNING);
						}
					}
					$query->select[$k] = "CASE " . implode( " ", $caseClauses) . " ELSE NULL END"
						.  " AS \"$k\"";
				}
			}
			

			$query->select[] = "\"$baseClass\".\"ID\"";
			$query->select[] = "CASE WHEN \"$baseClass\".\"ClassName\" IS NOT NULL THEN \"$baseClass\".\"ClassName\" ELSE '$baseClass' END AS \"RecordClassName\"";

			// Get the ClassName values to filter to
			$classNames = ClassInfo::subclassesFor($this->class);

			if(!$classNames) {
				user_error("DataObject::get() Can't find data sub-classes for '$callerClass'");
			}

			// If querying the base class, don't bother filtering on class name
			if($restrictClasses && $this->class != $baseClass) {
				// Get the ClassName values to filter to
				$classNames = ClassInfo::subclassesFor($this->class);
				if(!$classNames) {
					user_error("DataObject::get() Can't find data sub-classes for '$callerClass'");
				}

				$query->where[] = "\"$baseClass\".\"ClassName\" IN ('" . implode("','", $classNames) . "')";
			}
			self::$cache_buildSQL_query[$this->class] = clone $query;
		} else {
			$query = clone self::$cache_buildSQL_query[$this->class];
			
		}
		
		// Find a default sort
		if(!$sort) {
			$sort = $this->stat('default_sort');
		}
		// Add quoting to sort expression if it's a simple column name
		if(preg_match('/^[A-Z][A-Z0-9_]*$/i', $sort)) $sort = "\"$sort\"";

		$query->where($filter);
		$query->orderby($sort);
		$query->limit($limit);
		

		if($having) {
			$query->having[] = $having;
		}

		if($join) {
			$query->from[] = $join;
			// In order to group by unique columns we have to group by everything listed in the select
			foreach($query->select as $field) {
				// Skip the _SortColumns; these are only going to be aggregate functions
				if(preg_match('/AS\s+\"?_SortColumn/', $field, $matches)) {
				
				// Identify columns with aliases, and ignore the alias.  Making use of the alias in
				// group by was causing problems when those queries were subsequently passed into
				// SQLQuery::unlimitedRowCount.
				} else if(preg_match('/^(.*)\s+AS\s+(\"[^"]+\")\s*$/', $field, $matches)) {
					$query->groupby[] = $matches[1];
				// Otherwise just use the field as is
				} else {
					$query->groupby[] = $field;
				}
			}
		}

		return $query;
	}
	
	/**
	 * Cache for the hairy bit of buildSQL
	 */
	private static $cache_buildSQL_query;

	/**
	 * Like {@link buildSQL}, but applies the extension modifications.
	 * 
	 * @uses DataObjectDecorator->augmentSQL()
	 *
	 * @param string $filter A filter to be inserted into the WHERE clause.
	 * @param string|array $sort A sort expression to be inserted into the ORDER BY clause. If omitted, self::$default_sort will be used.
	 * @param string|array $limit A limit expression to be inserted into the LIMIT clause.
	 * @param string $join A single join clause. This can be used for filtering, only 1 instance of each DataObject will be returned.
	 * @param string $having A filter to be inserted into the HAVING clause.
	 * @return SQLQuery Query built
	 */
	public function extendedSQL($filter = "", $sort = "", $limit = "", $join = "", $having = ""){
		$query = $this->buildSQL($filter, $sort, $limit, $join, true, $having);
		$this->extend('augmentSQL', $query);
		return $query;
	}

	/**
	 * Return all objects matching the filter
	 * sub-classes are automatically selected and included
	 *
	 * @param string $callerClass The class of objects to be returned
	 * @param string $filter A filter to be inserted into the WHERE clause.
	 * @param string|array $sort A sort expression to be inserted into the ORDER BY clause.  If omitted, self::$default_sort will be used.
	 * @param string $join A single join clause.  This can be used for filtering, only 1 instance of each DataObject will be returned.
	 * @param string|array $limit A limit expression to be inserted into the LIMIT clause.
	 * @param string $containerClass The container class to return the results in.
	 *
	 * @return mixed The objects matching the filter, in the class specified by $containerClass
	 */
	public static function get($callerClass, $filter = "", $sort = "", $join = "", $limit = "", $containerClass = "DataObjectSet") {
		return singleton($callerClass)->instance_get($filter, $sort, $join, $limit, $containerClass);
	}

	/**
	 * The internal function that actually performs the querying for get().
	 * DataObject::get("Table","filter") is the same as singleton("Table")->instance_get("filter")
	 *
	 * @param string $filter A filter to be inserted into the WHERE clause.
	 * @param string $sort A sort expression to be inserted into the ORDER BY clause.  If omitted, self::$default_sort will be used.
	 * @param string $join A single join clause.  This can be used for filtering, only 1 instance of each DataObject will be returned.
	 * @param string $limit A limit expression to be inserted into the LIMIT clause.
	 * @param string $containerClass The container class to return the results in.
	 *
	 * @return mixed The objects matching the filter, in the class specified by $containerClass
	 */
	public function instance_get($filter = "", $sort = "", $join = "", $limit="", $containerClass = "DataObjectSet") {
		if(!DB::isActive()) {
			user_error("DataObjects have been requested before the database is ready. Please ensure your database connection details are correct, your database has been built, and that you are not trying to query the database in _config.php.", E_USER_ERROR);
		}
		
		$query = $this->extendedSQL($filter, $sort, $limit, $join);
		
		$records = $query->execute();
		
		$ret = $this->buildDataObjectSet($records, $containerClass, $query, $this->class);
		if($ret) $ret->parseQueryLimit($query);

		return $ret;
	}

	/**
	 * Take a database {@link SS_Query} and instanciate an object for each record.
	 *
	 * @param SS_Query|array $records The database records, a {@link SS_Query} object or an array of maps.
	 * @param string $containerClass The class to place all of the objects into.
	 *
	 * @return mixed The new objects in an object of type $containerClass
	 */
	function buildDataObjectSet($records, $containerClass = "DataObjectSet", $query = null, $baseClass = null) {
		foreach($records as $record) {
			if(empty($record['RecordClassName'])) {
				$record['RecordClassName'] = $record['ClassName'];
			}
			if(class_exists($record['RecordClassName'])) {
				$results[] = new $record['RecordClassName']($record);
			} else {
				if(!$baseClass) {
					user_error("Bad RecordClassName '{$record['RecordClassName']}' and "
						. "\$baseClass not set", E_USER_ERROR);
				} else if(!is_string($baseClass) || !class_exists($baseClass)) {
					user_error("Bad RecordClassName '{$record['RecordClassName']}' and bad "
						. "\$baseClass '$baseClass not set", E_USER_ERROR);
				}
				$results[] = new $baseClass($record);
			}
		}

		if(isset($results)) {
			return new $containerClass($results);
		}
	}

	/**
	 * A cache used by get_one.
	 * @var array
	 */
	protected static $cache_get_one;

	/**
	 * Return the first item matching the given query.
	 * All calls to get_one() are cached.
	 *
	 * @param string $callerClass The class of objects to be returned
	 * @param string $filter A filter to be inserted into the WHERE clause
	 * @param boolean $cache Use caching
	 * @param string $orderby A sort expression to be inserted into the ORDER BY clause.
	 *
	 * @return DataObject The first item matching the query
	 */
	public static function get_one($callerClass, $filter = "", $cache = true, $orderby = "") {
		$SNG = singleton($callerClass);

		$cacheKey = "{$filter}-{$orderby}";
		if($extra = $SNG->extend('cacheKeyComponent')) {
			$cacheKey .= '-' . implode("-", $extra);
		}
		$cacheKey = md5($cacheKey);
		
		// Flush destroyed items out of the cache
		if($cache && isset(DataObject::$cache_get_one[$callerClass][$cacheKey]) && DataObject::$cache_get_one[$callerClass][$cacheKey] instanceof DataObject && DataObject::$cache_get_one[$callerClass][$cacheKey]->destroyed) {
			DataObject::$cache_get_one[$callerClass][$cacheKey
			] = false;
		}
		if(!$cache || !isset(DataObject::$cache_get_one[$callerClass][$cacheKey])) {
			$item = $SNG->instance_get_one($filter, $orderby);
			if($cache) {
				DataObject::$cache_get_one[$callerClass][$cacheKey] = $item;
				if(!DataObject::$cache_get_one[$callerClass][$cacheKey]) {
					DataObject::$cache_get_one[$callerClass][$cacheKey] = false;
				}
			}
		}
		return $cache ? DataObject::$cache_get_one[$callerClass][$cacheKey] : $item;
	}

	/**
	 * Flush the cached results for all relations (has_one, has_many, many_many)
	 * Also clears any cached aggregate data
	 * 
	 * @param boolean $persistant When true will also clear persistant data stored in the Cache system.
	 *                            When false will just clear session-local cached data 
	 * 
	 */
	public function flushCache($persistant=true) {
		if($persistant) Aggregate::flushCache($this->class);
		
		if($this->class == 'DataObject') {
			DataObject::$cache_get_one = array();
			return;
		}

		$classes = ClassInfo::ancestry($this->class);
		foreach($classes as $class) {
			if(isset(self::$cache_get_one[$class])) unset(self::$cache_get_one[$class]);
		}
		
		$this->extend('flushCache');
		
		$this->componentCache = array();
	}

	static function flush_and_destroy_cache() {
		if(self::$cache_get_one) foreach(self::$cache_get_one as $class => $items) {
			if(is_array($items)) foreach($items as $item) {
				if($item) $item->destroy();
			}
		}
		self::$cache_get_one = array();
	}
	
	/**
	 * Reset internal caches, for example after test runs
	 */
	static function reset() {
		self::$cache_get_one = array();
		self::$cache_buildSQL_query = array();
	}

	/**
	 * Does the hard work for get_one()
	 * 
	 * @uses DataObjectDecorator->augmentSQL()
	 *
	 * @param string $filter A filter to be inserted into the WHERE clause
	 * @param string $orderby A sort expression to be inserted into the ORDER BY clause.
	 * @return DataObject The first item matching the query
	 */
	public function instance_get_one($filter, $orderby = null) {
		if(!DB::isActive()) {
			user_error("DataObjects have been requested before the database is ready. Please ensure your database connection details are correct, your database has been built, and that you are not trying to query the database in _config.php.", E_USER_ERROR);
		}
		
		$query = $this->buildSQL($filter);
		$query->limit = "1";
		if($orderby) {
			$query->orderby = $orderby;
		}

		$this->extend('augmentSQL', $query);

		$records = $query->execute();
		$records->rewind();
		$record = $records->current();

		if($record) {
			// Mid-upgrade, the database can have invalid RecordClassName values that need to be guarded against.
			if(class_exists($record['RecordClassName'])) {
				$record = new $record['RecordClassName']($record);
			} else {
				$record = new $this->class($record);
			}

			// Rather than restrict classes at the SQL-query level, we now check once the object has been instantiated
			// This lets us check up on weird errors where the class has been incorrectly set, and give warnings to our
			// developers
			return $record;
		}
	}

	/**
	 * Return the given element, searching by ID
	 *
	 * @param string $callerClass The class of the object to be returned
	 * @param int $id The id of the element
	 * @param boolean $cache See {@link get_one()}
	 *
	 * @return DataObject The element
	 */
	public static function get_by_id($callerClass, $id, $cache = true) {
		if(is_numeric($id)) {
			if(is_subclass_of($callerClass, 'DataObject')) {
				$tableClasses = ClassInfo::dataClassesFor($callerClass);
				$baseClass = array_shift($tableClasses);
				return DataObject::get_one($callerClass,"\"$baseClass\".\"ID\" = $id", $cache);

				// This simpler code will be used by non-DataObject classes that implement DataObjectInterface
			} else {
				return DataObject::get_one($callerClass,"\"ID\" = $id", $cache);
			}
		} else {
			user_error("DataObject::get_by_id passed a non-numeric ID #$id", E_USER_WARNING);
		}
	}

	/**
	 * Get the name of the base table for this object
	 */
	public function baseTable() {
		$tableClasses = ClassInfo::dataClassesFor($this->class);
		return array_shift($tableClasses);
	}

	//-------------------------------------------------------------------------------------------//

	/**
	 * Return the database indexes on this table.
	 * This array is indexed by the name of the field with the index, and
	 * the value is the type of index.
	 */
	public function databaseIndexes() {
		$has_one = $this->uninherited('has_one',true);
		$classIndexes = $this->uninherited('indexes',true);
		//$fileIndexes = $this->uninherited('fileIndexes', true);

		$indexes = array();

		if($has_one) {
			foreach($has_one as $relationshipName => $fieldType) {
				$indexes[$relationshipName . 'ID'] = true;
			}
		}

		if($classIndexes) {
			foreach($classIndexes as $indexName => $indexType) {
				$indexes[$indexName] = $indexType;
			}
		}

		if(get_parent_class($this) == "DataObject") {
			$indexes['ClassName'] = true;
		}

		return $indexes;
	}

	/**
	 * Check the database schema and update it as necessary.
	 * 
	 * @uses DataObjectDecorator->augmentDatabase()
	 */
	public function requireTable() {
		// Only build the table if we've actually got fields
		$fields = self::database_fields($this->class);
		$extensions = self::database_extensions($this->class);
		
		$indexes = $this->databaseIndexes();

		if($fields) {
			$hasAutoIncPK = ($this->class == ClassInfo::baseDataClass($this->class));
			DB::requireTable($this->class, $fields, $indexes, $hasAutoIncPK, $this->stat('create_table_options'), $extensions);
		} else {
			DB::dontRequireTable($this->class);
		}

		// Build any child tables for many_many items
		if($manyMany = $this->uninherited('many_many', true)) {
			$extras = $this->uninherited('many_many_extraFields', true);
			foreach($manyMany as $relationship => $childClass) {
				// Build field list
				$manymanyFields = array(
					"{$this->class}ID" => "Int",
				(($this->class == $childClass) ? "ChildID" : "{$childClass}ID") => "Int",
				);
				if(isset($extras[$relationship])) {
					$manymanyFields = array_merge($manymanyFields, $extras[$relationship]);
				}

				// Build index list
				$manymanyIndexes = array(
					"{$this->class}ID" => true,
				(($this->class == $childClass) ? "ChildID" : "{$childClass}ID") => true,
				);
				
				DB::requireTable("{$this->class}_$relationship", $manymanyFields, $manymanyIndexes, true, null, $extensions);
			}
		}

		// Let any extentions make their own database fields
		$this->extend('augmentDatabase', $dummy);
	}

	/**
	 * Add default records to database. This function is called whenever the
	 * database is built, after the database tables have all been created. Overload
	 * this to add default records when the database is built, but make sure you
	 * call parent::requireDefaultRecords().
	 * 
	 * @uses DataObjectDecorator->requireDefaultRecords()
	 */
	public function requireDefaultRecords() {
		$defaultRecords = $this->stat('default_records');

		if(!empty($defaultRecords)) {
			$hasData = DataObject::get_one($this->class);
			if(!$hasData) {
				$className = $this->class;
				foreach($defaultRecords as $record) {
					$obj = new $className($record);
					$obj->write();
				}
				DB::alteration_message("Added default records to $className table","created");
			}
		}
		
		// Let any extentions make their own database default data
		$this->extend('requireDefaultRecords', $dummy);
	}
	
	/**
	 * @see DataObject::database_fields()
	 */
	public function databaseFields() {
		user_error("databaseFields() is deprecated; use self::database_fields() "
			. "instead", E_USER_NOTICE);
		return self::database_fields($this->class);
	}
	
	/**
	 * @see DataObject::custom_database_fields()
	 */
	public function customDatabaseFields() {
		user_error("customDatabaseFields() is deprecated; use self::custom_database_fields() "
			. "instead", E_USER_NOTICE);
		return self::custom_database_fields($this->class);
	}
	
	/**
	 * Returns fields bu traversing the class heirachy in a bottom-up direction.
	 *
	 * Needed to avoid getCMSFields being empty when customDatabaseFields overlooks
	 * the inheritance chain of the $db array, where a child data object has no $db array,
	 * but still needs to know the properties of its parent. This should be merged into databaseFields or
	 * customDatabaseFields.
	 *
	 * @todo review whether this is still needed after recent API changes
	 */
	public function inheritedDatabaseFields() {
		$fields     = array();
		$currentObj = $this->class;
		
		while($currentObj != 'DataObject') {
			$fields     = array_merge($fields, self::custom_database_fields($currentObj));
			$currentObj = get_parent_class($currentObj);
		}
		
		return (array) $fields;
	}

	/**
	 * Get the default searchable fields for this object,
	 * as defined in the $searchable_fields list. If searchable
	 * fields are not defined on the data object, uses a default
	 * selection of summary fields.
	 *
	 * @return array
	 */
	public function searchableFields() {
		// can have mixed format, need to make consistent in most verbose form
		$fields = $this->stat('searchable_fields');
		
		$labels = $this->fieldLabels();
		
		// fallback to summary fields
		if(!$fields) $fields = array_keys($this->summaryFields());
		
		// we need to make sure the format is unified before
		// augmenting fields, so decorators can apply consistent checks
		// but also after augmenting fields, because the decorator
		// might use the shorthand notation as well

		// rewrite array, if it is using shorthand syntax
		$rewrite = array();
		foreach($fields as $name => $specOrName) {
			$identifer = (is_int($name)) ? $specOrName : $name;

			if(is_int($name)) {
				// Format: array('MyFieldName')
				$rewrite[$identifer] = array();
			} elseif(is_array($specOrName)) {
				// Format: array('MyFieldName' => array(
				//   'filter => 'ExactMatchFilter',
				//   'field' => 'NumericField', // optional
				//   'title' => 'My Title', // optiona.
				// ))
				$rewrite[$identifer] = array_merge(
					array('filter' => $this->relObject($identifer)->stat('default_search_filter_class')),
					(array)$specOrName
				);
			} else {
				// Format: array('MyFieldName' => 'ExactMatchFilter')
				$rewrite[$identifer] = array(
					'filter' => $specOrName,
				);
			}
			if(!isset($rewrite[$identifer]['title'])) {
				$rewrite[$identifer]['title'] = (isset($labels[$identifer])) ? $labels[$identifer] : FormField::name_to_label($identifer);
			}
			if(!isset($rewrite[$identifer]['filter'])) {
				$rewrite[$identifer]['filter'] = 'PartialMatchFilter';
			}
		}

		$fields = $rewrite;
		
		// apply DataObjectDecorators if present
		$this->extend('updateSearchableFields', $fields);

		return $fields;
	}
	
	/**
	 * Get any user defined searchable fields labels that
	 * exist. Allows overriding of default field names in the form
	 * interface actually presented to the user.
	 *
	 * The reason for keeping this separate from searchable_fields,
	 * which would be a logical place for this functionality, is to
	 * avoid bloating and complicating the configuration array. Currently
	 * much of this system is based on sensible defaults, and this property
	 * would generally only be set in the case of more complex relationships
	 * between data object being required in the search interface.
	 *
	 * Generates labels based on name of the field itself, if no static property 
	 * {@link self::field_labels} exists.
	 *
	 * @uses $field_labels
	 * @uses FormField::name_to_label()
	 *
	 * @param boolean $includerelations a boolean value to indicate if the labels returned include relation fields
	 * 
	 * @return array|string Array of all element labels if no argument given, otherwise the label of the field
	 */
	public function fieldLabels($includerelations = true) {
		$customLabels = $this->stat('field_labels');
		$autoLabels = array();
		
		// get all translated static properties as defined in i18nCollectStatics()
		$ancestry = ClassInfo::ancestry($this->class);
		$ancestry = array_reverse($ancestry);
		if($ancestry) foreach($ancestry as $ancestorClass) {
			if($ancestorClass == 'ViewableData') break;
			$types = array(
				'db'        => (array) Object::uninherited_static($ancestorClass, 'db'),
			);
			if($includerelations){
				$types['has_one'] = (array)singleton($ancestorClass)->uninherited('has_one', true);
				$types['has_many'] = (array)singleton($ancestorClass)->uninherited('has_many', true);
				$types['many_many'] = (array)singleton($ancestorClass)->uninherited('many_many', true);
			}
			foreach($types as $type => $attrs) {
				foreach($attrs as $name => $spec)
				$autoLabels[$name] = _t("{$ancestorClass}.{$type}_{$name}",FormField::name_to_label($name));
 			}
 		}

		$labels = array_merge((array)$autoLabels, (array)$customLabels);
		
		$this->extend('updateFieldLabels', $labels);

		return $labels;
	}
	
	/**
	 * Get a human-readable label for a single field,
	 * see {@link fieldLabels()} for more details.
	 * 
	 * @uses fieldLabels()
	 * @uses FormField::name_to_label()
	 * 
	 * @param string $name Name of the field
	 * @return string Label of the field
	 */
	public function fieldLabel($name) {
		$labels = $this->fieldLabels();
		return (isset($labels[$name])) ? $labels[$name] : FormField::name_to_label($name);
	}

	/**
	 * Get the default summary fields for this object.
	 *
	 * @todo use the translation apparatus to return a default field selection for the language
	 *
	 * @return array
	 */
	public function summaryFields(){

		$fields = $this->stat('summary_fields');

		// if fields were passed in numeric array,
		// convert to an associative array
		if($fields && array_key_exists(0, $fields)) {
			$fields = array_combine(array_values($fields), array_values($fields));
		}

		if (!$fields) {
			$fields = array();
			// try to scaffold a couple of usual suspects
			if ($this->hasField('Name')) $fields['Name'] = 'Name';
			if ($this->hasDataBaseField('Title')) $fields['Title'] = 'Title';
			if ($this->hasField('Description')) $fields['Description'] = 'Description';
			if ($this->hasField('FirstName')) $fields['FirstName'] = 'First Name';
		}
		$this->extend("updateSummaryFields", $fields);
		
		// Final fail-over, just list ID field
		if(!$fields) $fields['ID'] = 'ID';
		
		return $fields;
	}

	/**
	 * Defines a default list of filters for the search context.
	 *
	 * If a filter class mapping is defined on the data object,
	 * it is constructed here. Otherwise, the default filter specified in
	 * {@link DBField} is used.
	 *
	 * @todo error handling/type checking for valid FormField and SearchFilter subclasses?
	 *
	 * @return array
	 */
	public function defaultSearchFilters() {
		$filters = array();
		foreach($this->searchableFields() as $name => $spec) {
			$filterClass = $spec['filter'];
			// if $filterClass is not set a name of any subclass of SearchFilter than assing 'PartiailMatchFilter' to it
			if (!is_subclass_of($filterClass, 'SearchFilter')) {
				$filterClass = 'PartialMatchFilter';
			}
			$filters[$name] = new $filterClass($name);
		}
		return $filters;
	}

	/**
	 * @return boolean True if the object is in the database
	 */
	public function isInDB() {
		return is_numeric( $this->ID ) && $this->ID > 0;
	}

	/**
	 * Sets a 'context object' that can be used to provide hints about how to process a particular get / get_one request.
	 * In particular, DataObjectDecorators can use this to amend queries more effectively.
	 * Care must be taken to unset the context object after you're done with it, otherwise you will have a stale context,
	 * which could cause horrible bugs.
	 */
	public static function set_context_obj($obj) {
		if($obj && self::$context_obj) user_error("Dataobject::set_context_obj passed " . $obj->class . "." . $obj->ID . " when there is already a context: " . self::$context_obj->class . '.' . self::$context_obj->ID, E_USER_WARNING);
		self::$context_obj = $obj;
	}

	/**
	 * Retrieve the current context object.
	 */
	public static function context_obj() {
		return self::$context_obj;
	}

	/**
	 * @ignore
	 */
	protected static $context_obj = null;

	/*
	 * @ignore
	 */
	private static $subclass_access = true; 
	
	/**
	 * Temporarily disable subclass access in data object qeur
	 */
	static function disable_subclass_access() {
		self::$subclass_access = false;
	}
	static function enable_subclass_access() {
		self::$subclass_access = true;
	}
	
	//-------------------------------------------------------------------------------------------//

	/**
	 * Database field definitions.
	 * This is a map from field names to field type. The field
	 * type should be a class that extends .
	 * @var array
	 */
	public static $db = null;

	/**
	 * Use a casting object for a field. This is a map from
	 * field name to class name of the casting object.
	 * @var array
	 */
	public static $casting = array(
		"LastEdited" => "SS_Datetime",
		"Created" => "SS_Datetime",
		"Title" => 'Text',
	);
	
	/**
	 * Specify custom options for a CREATE TABLE call.
	 * Can be used to specify a custom storage engine for specific database table.
	 * All options have to be keyed for a specific database implementation,
	 * identified by their class name (extending from {@link SS_Database}).
	 * 
	 * <code>
	 * array(
	 * 	'MySQLDatabase' => 'ENGINE=MyISAM'
	 * )
	 * </code>
	 *
	 * Caution: This API is experimental, and might not be
	 * included in the next major release. Please use with care.
	 * 
	 * @var array
	 */
	static $create_table_options = array(
		'MySQLDatabase' => 'ENGINE=MyISAM'
	);

	/**
	 * If a field is in this array, then create a database index
	 * on that field. This is a map from fieldname to index type.
	 * See {@link SS_Database->requireIndex()} and custom subclasses for details on the array notation.
	 * 
	 * @var array
	 */
	public static $indexes = null;

	/**
	 * Inserts standard column-values when a DataObject
	 * is instanciated. Does not insert default records {@see $default_records}.
	 * This is a map from fieldname to default value.
	 * 
	 *  - If you would like to change a default value in a sub-class, just specify it.
	 *  - If you would like to disable the default value given by a parent class, set the default value to 0,'',or false in your
	 *    subclass.  Setting it to null won't work.
	 * 
	 * @var array
	 */
	public static $defaults = null;

	/**
	 * Multidimensional array which inserts default data into the database
	 * on a db/build-call as long as the database-table is empty. Please use this only
	 * for simple constructs, not for SiteTree-Objects etc. which need special
	 * behaviour such as publishing and ParentNodes.
	 *
	 * Example:
	 * array(
	 * 	array('Title' => "DefaultPage1", 'PageTitle' => 'page1'),
	 * 	array('Title' => "DefaultPage2")
	 * ).
	 *
	 * @var array
	 */
	public static $default_records = null;

	/**
	 * One-to-zero relationship defintion. This is a map of component name to data type. In order to turn this into a
	 * true one-to-one relationship you can add a {@link DataObject::$belongs_to} relationship on the child class.
	 *
	 * Note that you cannot have a has_one and belongs_to relationship with the same name.
	 *
	 *	@var array
	 */
	public static $has_one = null;
	
	/**
	 * A meta-relationship that allows you to define the reverse side of a {@link DataObject::$has_one}.
	 *
	 * This does not actually create any data structures, but allows you to query the other object in a one-to-one
	 * relationship from the child object. If you have multiple belongs_to links to another object you can use the
	 * syntax "ClassName.HasOneName" to specify which foreign has_one key on the other object to use.
	 *
	 * Note that you cannot have a has_one and belongs_to relationship with the same name.
	 *
	 * @var array
	 */
	public static $belongs_to;
	
	/**
	 * This defines a one-to-many relationship. It is a map of component name to the remote data class.
	 *
	 * This relationship type does not actually create a data structure itself - you need to define a matching $has_one
	 * relationship on the child class. Also, if the $has_one relationship on the child class has multiple links to this
	 * class you can use the syntax "ClassName.HasOneRelationshipName" in the remote data class definition to show
	 * which foreign key to use.
	 *
	 * @var array
	 */
	public static $has_many = null;

	/**
	 * many-many relationship definitions.
	 * This is a map from component name to data type.
	 * @var array
	 */
	public static $many_many = null;

	/**
	 * Extra fields to include on the connecting many-many table.
	 * This is a map from field name to field type.
	 * 
	 * Example code:
	 * <code>
	 * public static $many_many_extraFields = array(
	 * 	'Members' => array(
	 *			'Role' => 'Varchar(100)'
	 *		)
	 * );
	 * </code>
	 * 
	 * @var array
	 */
	public static $many_many_extraFields = null;

	/**
	 * The inverse side of a many-many relationship.
	 * This is a map from component name to data type.
	 * @var array
	 */
	public static $belongs_many_many = null;

	/**
	 * The default sort expression. This will be inserted in the ORDER BY
	 * clause of a SQL query if no other sort expression is provided.
	 * @var string
	 */
	public static $default_sort = null;

	/**
	 * Default list of fields that can be scaffolded by the ModelAdmin
	 * search interface.
	 *
	 * Overriding the default filter, with a custom defined filter:
	 * <code>
	 * 	static $searchable_fields = array(
	 * 	   "Name" => "PartialMatchFilter"
	 *  );
	 * </code>
	 * 
	 * Overriding the default form fields, with a custom defined field.
	 * The 'filter' parameter will be generated from {@link DBField::$default_search_filter_class}.
	 * The 'title' parameter will be generated from {@link DataObject->fieldLabels()}.
	 * <code>
	 * 	static $searchable_fields = array(
	 * 	   "Name" => array(
	 * 			"field" => "TextField"
	 * 		)
	 *  );
	 * </code>
	 *
	 * Overriding the default form field, filter and title:
	 * <code>
	 * 	static $searchable_fields = array(
	 * 	   "Organisation.ZipCode" => array(
	 * 			"field" => "TextField", 
	 * 			"filter" => "PartialMatchFilter",
	 * 			"title" => 'Organisation ZIP'
	 * 		)
	 *  );
	 * </code>
	 */
	public static $searchable_fields = null;

	/**
	 * User defined labels for searchable_fields, used to override
	 * default display in the search form.
	 */
	public static $field_labels = null;

	/**
	 * Provides a default list of fields to be used by a 'summary'
	 * view of this object.
	 */
	public static $summary_fields = null;
	
	/**
	 * Provides a list of allowed methods that can be called via RESTful api.
	 */
	public static $allowed_actions = null;
	
	/**
	 * Collect all static properties on the object
	 * which contain natural language, and need to be translated.
	 * The full entity name is composed from the class name and a custom identifier.
	 * 
	 * @return array A numerical array which contains one or more entities in array-form.
	 * Each numeric entity array contains the "arguments" for a _t() call as array values:
	 * $entity, $string, $priority, $context.
	 */
	public function provideI18nEntities() {
		$entities = array();
		
		$entities["{$this->class}.SINGULARNAME"] = array(
			$this->singular_name(),
			PR_MEDIUM,
			'Singular name of the object, used in dropdowns and to generally identify a single object in the interface'
		);

		$entities["{$this->class}.PLURALNAME"] = array(
			$this->plural_name(),
			PR_MEDIUM,
			'Pural name of the object, used in dropdowns and to generally identify a collection of this object in the interface'
		);
		
		return $entities;
	}
	
	/**
 	 * Returns true if the given method/parameter has a value
 	 * (Uses the DBField::hasValue if the parameter is a database field)
 	 * 
	 * @param string $field The field name
	 * @param array $arguments
	 * @param bool $cache
 	 * @return boolean
 	 */
 	function hasValue($field, $arguments = null, $cache = true) {
 		$obj = $this->dbObject($field);
 		if($obj) {
 			return $obj->hasValue();
 		} else {
 			return parent::hasValue($field, $arguments, $cache);
 		}
 	}

}