<?php
/*
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * This software consists of voluntary contributions made by many individuals
 * and is licensed under the LGPL. For more information, see
 * <http://www.doctrine-project.org>.
 */

namespace Doctrine\ORM;

use Exception, InvalidArgumentException, UnexpectedValueException,
    Doctrine\Common\Collections\ArrayCollection,
    Doctrine\Common\Collections\Collection,
    Doctrine\Common\NotifyPropertyChanged,
    Doctrine\Common\PropertyChangedListener,
    Doctrine\ORM\Event\LifecycleEventArgs,
    Doctrine\ORM\Mapping\ClassMetadata,
    Doctrine\ORM\Proxy\Proxy;

/**
 * The UnitOfWork is responsible for tracking changes to objects during an
 * "object-level" transaction and for writing out changes to the database
 * in the correct order.
 *
 * @since       2.0
 * @author      Benjamin Eberlei <kontakt@beberlei.de>
 * @author      Guilherme Blanco <guilhermeblanco@hotmail.com>
 * @author      Jonathan Wage <jonwage@gmail.com>
 * @author      Roman Borschel <roman@code-factory.org>
 * @internal    This class contains highly performance-sensitive code.
 */
class UnitOfWork implements PropertyChangedListener
{
    /**
     * An entity is in MANAGED state when its persistence is managed by an EntityManager.
     */
    const STATE_MANAGED = 1;

    /**
     * An entity is new if it has just been instantiated (i.e. using the "new" operator)
     * and is not (yet) managed by an EntityManager.
     */
    const STATE_NEW = 2;

    /**
     * A detached entity is an instance with persistent state and identity that is not
     * (or no longer) associated with an EntityManager (and a UnitOfWork).
     */
    const STATE_DETACHED = 3;

    /**
     * A removed entity instance is an instance with a persistent identity,
     * associated with an EntityManager, whose persistent state will be deleted
     * on commit.
     */
    const STATE_REMOVED = 4;

    /**
     * The identity map that holds references to all managed entities that have
     * an identity. The entities are grouped by their class name.
     * Since all classes in a hierarchy must share the same identifier set,
     * we always take the root class name of the hierarchy.
     *
     * @var array
     */
    private $identityMap = array();

    /**
     * Map of all identifiers of managed entities.
     * Keys are object ids (spl_object_hash).
     *
     * @var array
     */
    private $entityIdentifiers = array();

    /**
     * Map of the original entity data of managed entities.
     * Keys are object ids (spl_object_hash). This is used for calculating changesets
     * at commit time.
     *
     * @var array
     * @internal Note that PHPs "copy-on-write" behavior helps a lot with memory usage.
     *           A value will only really be copied if the value in the entity is modified
     *           by the user.
     */
    private $originalEntityData = array();

    /**
     * Map of entity changes. Keys are object ids (spl_object_hash).
     * Filled at the beginning of a commit of the UnitOfWork and cleaned at the end.
     *
     * @var array
     */
    private $entityChangeSets = array();

    /**
     * The (cached) states of any known entities.
     * Keys are object ids (spl_object_hash).
     *
     * @var array
     */
    private $entityStates = array();

    /**
     * Map of entities that are scheduled for dirty checking at commit time.
     * This is only used for entities with a change tracking policy of DEFERRED_EXPLICIT.
     * Keys are object ids (spl_object_hash).
     * 
     * @var array
     * @todo rename: scheduledForSynchronization
     */
    private $scheduledForDirtyCheck = array();

    /**
     * A list of all pending entity insertions.
     *
     * @var array
     */
    private $entityInsertions = array();

    /**
     * A list of all pending entity updates.
     *
     * @var array
     */
    private $entityUpdates = array();
    
    /**
     * Any pending extra updates that have been scheduled by persisters.
     * 
     * @var array
     */
    private $extraUpdates = array();

    /**
     * A list of all pending entity deletions.
     *
     * @var array
     */
    private $entityDeletions = array();

    /**
     * All pending collection deletions.
     *
     * @var array
     */
    private $collectionDeletions = array();

    /**
     * All pending collection updates.
     *
     * @var array
     */
    private $collectionUpdates = array();

    /**
     * List of collections visited during changeset calculation on a commit-phase of a UnitOfWork.
     * At the end of the UnitOfWork all these collections will make new snapshots
     * of their data.
     *
     * @var array
     */
    private $visitedCollections = array();

    /**
     * The EntityManager that "owns" this UnitOfWork instance.
     *
     * @var Doctrine\ORM\EntityManager
     */
    private $em;

    /**
     * The calculator used to calculate the order in which changes to
     * entities need to be written to the database.
     *
     * @var Doctrine\ORM\Internal\CommitOrderCalculator
     */
    private $commitOrderCalculator;

    /**
     * The entity persister instances used to persist entity instances.
     *
     * @var array
     */
    private $persisters = array();

    /**
     * The collection persister instances used to persist collections.
     *
     * @var array
     */
    private $collectionPersisters = array();
    
    /**
     * The EventManager used for dispatching events.
     * 
     * @var EventManager
     */
    private $evm;
    
    /**
     * Orphaned entities that are scheduled for removal.
     * 
     * @var array
     */
    private $orphanRemovals = array();
    
    //private $_readOnlyObjects = array();

    /**
     * Map of Entity Class-Names and corresponding IDs that should eager loaded when requested.
     * 
     * @var array
     */
    private $eagerLoadingEntities = array();

    /**
     * Initializes a new UnitOfWork instance, bound to the given EntityManager.
     *
     * @param Doctrine\ORM\EntityManager $em
     */
    public function __construct(EntityManager $em)
    {
        $this->em = $em;
        $this->evm = $em->getEventManager();
    }

    /**
     * Commits the UnitOfWork, executing all operations that have been postponed
     * up to this point. The state of all managed entities will be synchronized with
     * the database.
     * 
     * The operations are executed in the following order:
     * 
     * 1) All entity insertions
     * 2) All entity updates
     * 3) All collection deletions
     * 4) All collection updates
     * 5) All entity deletions
     * 
     */
    public function commit()
    {
        // Compute changes done since last commit.
        $this->computeChangeSets();

        if ( ! ($this->entityInsertions ||
                $this->entityDeletions ||
                $this->entityUpdates ||
                $this->collectionUpdates ||
                $this->collectionDeletions ||
                $this->orphanRemovals)) {
            return; // Nothing to do.
        }

        if ($this->orphanRemovals) {
            foreach ($this->orphanRemovals as $orphan) {
                $this->remove($orphan);
            }
        }
        
        // Raise onFlush
        if ($this->evm->hasListeners(Events::onFlush)) {
            $this->evm->dispatchEvent(Events::onFlush, new Event\OnFlushEventArgs($this->em));
        }
        
        // Now we need a commit order to maintain referential integrity
        $commitOrder = $this->getCommitOrder();

        $conn = $this->em->getConnection();

        $conn->beginTransaction();
        try {
            if ($this->entityInsertions) {
                foreach ($commitOrder as $class) {
                    $this->executeInserts($class);
                }
            }

            if ($this->entityUpdates) {
                foreach ($commitOrder as $class) {
                    $this->executeUpdates($class);
                }
            }

            // Extra updates that were requested by persisters.
            if ($this->extraUpdates) {
                $this->executeExtraUpdates();
            }

            // Collection deletions (deletions of complete collections)
            foreach ($this->collectionDeletions as $collectionToDelete) {
                $this->getCollectionPersister($collectionToDelete->getMapping())
                        ->delete($collectionToDelete);
            }
            // Collection updates (deleteRows, updateRows, insertRows)
            foreach ($this->collectionUpdates as $collectionToUpdate) {
                $this->getCollectionPersister($collectionToUpdate->getMapping())
                        ->update($collectionToUpdate);
            }

            // Entity deletions come last and need to be in reverse commit order
            if ($this->entityDeletions) {
                for ($count = count($commitOrder), $i = $count - 1; $i >= 0; --$i) {
                    $this->executeDeletions($commitOrder[$i]);
                }
            }

            $conn->commit();
        } catch (Exception $e) {
            $this->em->close();
            $conn->rollback();
            throw $e;
        }

        // Take new snapshots from visited collections
        foreach ($this->visitedCollections as $coll) {
            $coll->takeSnapshot();
        }

        // Clear up
        $this->entityInsertions =
        $this->entityUpdates =
        $this->entityDeletions =
        $this->extraUpdates =
        $this->entityChangeSets =
        $this->collectionUpdates =
        $this->collectionDeletions =
        $this->visitedCollections =
        $this->scheduledForDirtyCheck =
        $this->orphanRemovals = array();
    }
    
    /**
     * Executes any extra updates that have been scheduled.
     */
    private function executeExtraUpdates()
    {
        foreach ($this->extraUpdates as $oid => $update) {
            list ($entity, $changeset) = $update;
            $this->entityChangeSets[$oid] = $changeset;
            $this->getEntityPersister(get_class($entity))->update($entity);
        }
    }

    /**
     * Gets the changeset for an entity.
     *
     * @return array
     */
    public function getEntityChangeSet($entity)
    {
        $oid = spl_object_hash($entity);
        if (isset($this->entityChangeSets[$oid])) {
            return $this->entityChangeSets[$oid];
        }
        return array();
    }

    /**
     * Computes the changes that happened to a single entity.
     *
     * Modifies/populates the following properties:
     *
     * {@link _originalEntityData}
     * If the entity is NEW or MANAGED but not yet fully persisted (only has an id)
     * then it was not fetched from the database and therefore we have no original
     * entity data yet. All of the current entity data is stored as the original entity data.
     *
     * {@link _entityChangeSets}
     * The changes detected on all properties of the entity are stored there.
     * A change is a tuple array where the first entry is the old value and the second
     * entry is the new value of the property. Changesets are used by persisters
     * to INSERT/UPDATE the persistent entity state.
     *
     * {@link _entityUpdates}
     * If the entity is already fully MANAGED (has been fetched from the database before)
     * and any changes to its properties are detected, then a reference to the entity is stored
     * there to mark it for an update.
     *
     * {@link _collectionDeletions}
     * If a PersistentCollection has been de-referenced in a fully MANAGED entity,
     * then this collection is marked for deletion.
     *
     * @param ClassMetadata $class The class descriptor of the entity.
     * @param object $entity The entity for which to compute the changes.
     */
    public function computeChangeSet(ClassMetadata $class, $entity)
    {
        if ( ! $class->isInheritanceTypeNone()) {
            $class = $this->em->getClassMetadata(get_class($entity));
        }
        
        $oid = spl_object_hash($entity);
        $actualData = array();
        foreach ($class->reflFields as $name => $refProp) {
            $value = $refProp->getValue($entity);
            if (isset($class->associationMappings[$name])
                    && ($class->associationMappings[$name]['type'] & ClassMetadata::TO_MANY)
                    && $value !== null
                    && ! ($value instanceof PersistentCollection)) {

                // If $value is not a Collection then use an ArrayCollection.
                if ( ! $value instanceof Collection) {
                    $value = new ArrayCollection($value);
                }
                
                $assoc = $class->associationMappings[$name];
                
                // Inject PersistentCollection
                $coll = new PersistentCollection(
                    $this->em,
                    $this->em->getClassMetadata($assoc['targetEntity']),
                    $value
                );
                
                $coll->setOwner($entity, $assoc);
                $coll->setDirty( ! $coll->isEmpty());
                $class->reflFields[$name]->setValue($entity, $coll);
                $actualData[$name] = $coll;
            } else if ( (! $class->isIdentifier($name) || ! $class->isIdGeneratorIdentity()) && ($name !== $class->versionField) ) {
                $actualData[$name] = $value;
            }
        }

        if ( ! isset($this->originalEntityData[$oid])) {
            // Entity is either NEW or MANAGED but not yet fully persisted (only has an id).
            // These result in an INSERT.
            $this->originalEntityData[$oid] = $actualData;
            $changeSet = array();
            foreach ($actualData as $propName => $actualValue) {
                if (isset($class->associationMappings[$propName])) {
                    $assoc = $class->associationMappings[$propName];
                    if ($assoc['isOwningSide'] && $assoc['type'] & ClassMetadata::TO_ONE) {
                        $changeSet[$propName] = array(null, $actualValue);
                    }
                } else {
                    $changeSet[$propName] = array(null, $actualValue);
                }
            }
            $this->entityChangeSets[$oid] = $changeSet;
        } else {
            // Entity is "fully" MANAGED: it was already fully persisted before
            // and we have a copy of the original data
            $originalData = $this->originalEntityData[$oid];
            $isChangeTrackingNotify = $class->isChangeTrackingNotify();
            $changeSet = ($isChangeTrackingNotify && isset($this->entityChangeSets[$oid])) ? $this->entityChangeSets[$oid] : array();

            foreach ($actualData as $propName => $actualValue) {
                $orgValue = isset($originalData[$propName]) ? $originalData[$propName] : null;
                if (isset($class->associationMappings[$propName])) {
                    $assoc = $class->associationMappings[$propName];
                    if ($assoc['type'] & ClassMetadata::TO_ONE && $orgValue !== $actualValue) {
                        if ($assoc['isOwningSide']) {
                            $changeSet[$propName] = array($orgValue, $actualValue);
                        }
                        if ($orgValue !== null && $assoc['orphanRemoval']) {
                            $this->scheduleOrphanRemoval($orgValue);
                        }
                    } else if ($orgValue instanceof PersistentCollection && $orgValue !== $actualValue) {
                        // A PersistentCollection was de-referenced, so delete it.
                        if  ( ! in_array($orgValue, $this->collectionDeletions, true)) {
                            $this->collectionDeletions[] = $orgValue;
                            $changeSet[$propName] = $orgValue; // Signal changeset, to-many assocs will be ignored.
                        }
                    }
                } else if ($isChangeTrackingNotify) {
                    continue;
                } else if ($orgValue !== $actualValue) {
                    $changeSet[$propName] = array($orgValue, $actualValue);
                }
            }
            if ($changeSet) {
                $this->entityChangeSets[$oid] = $changeSet;
                $this->originalEntityData[$oid] = $actualData;
                $this->entityUpdates[$oid] = $entity;
            }
        }

        // Look for changes in associations of the entity
        foreach ($class->associationMappings as $field => $assoc) {
            $val = $class->reflFields[$field]->getValue($entity);
            if ($val !== null) {
                $this->computeAssociationChanges($assoc, $val);
            }
        }
    }

    /**
     * Computes all the changes that have been done to entities and collections
     * since the last commit and stores these changes in the _entityChangeSet map
     * temporarily for access by the persisters, until the UoW commit is finished.
     */
    public function computeChangeSets()
    {
        // Compute changes for INSERTed entities first. This must always happen.
        foreach ($this->entityInsertions as $entity) {
            $class = $this->em->getClassMetadata(get_class($entity));
            $this->computeChangeSet($class, $entity);
        }

        // Compute changes for other MANAGED entities. Change tracking policies take effect here.
        foreach ($this->identityMap as $className => $entities) {
            $class = $this->em->getClassMetadata($className);

            // Skip class if instances are read-only
            if ($class->isReadOnly) {
                continue;
            }

            // If change tracking is explicit or happens through notification, then only compute
            // changes on entities of that type that are explicitly marked for synchronization.
            $entitiesToProcess = ! $class->isChangeTrackingDeferredImplicit() ?
                    (isset($this->scheduledForDirtyCheck[$className]) ?
                        $this->scheduledForDirtyCheck[$className] : array())
                    : $entities;

            foreach ($entitiesToProcess as $entity) {
                // Ignore uninitialized proxy objects
                if (/* $entity is readOnly || */ $entity instanceof Proxy && ! $entity->__isInitialized__) {
                    continue;
                }
                // Only MANAGED entities that are NOT SCHEDULED FOR INSERTION are processed here.
                $oid = spl_object_hash($entity);
                if ( ! isset($this->entityInsertions[$oid]) && isset($this->entityStates[$oid])) {
                    $this->computeChangeSet($class, $entity);
                }
            }
        }
    }

    /**
     * Computes the changes of an association.
     *
     * @param AssociationMapping $assoc
     * @param mixed $value The value of the association.
     */
    private function computeAssociationChanges($assoc, $value)
    {
        if ($value instanceof PersistentCollection && $value->isDirty()) {
            if ($assoc['isOwningSide']) {
                $this->collectionUpdates[] = $value;
            }
            $this->visitedCollections[] = $value;
        }

        // Look through the entities, and in any of their associations, for transient (new)
        // enities, recursively. ("Persistence by reachability")
        if ($assoc['type'] & ClassMetadata::TO_ONE) {
            if ($value instanceof Proxy && ! $value->__isInitialized__) {
                return; // Ignore uninitialized proxy objects
            }
            $value = array($value);
        } else if ($value instanceof PersistentCollection) {
            // Unwrap. Uninitialized collections will simply be empty.
            $value = $value->unwrap();
        }

        $targetClass = $this->em->getClassMetadata($assoc['targetEntity']);
        foreach ($value as $entry) {
            $state = $this->getEntityState($entry, self::STATE_NEW);
            $oid = spl_object_hash($entry);
            if ($state == self::STATE_NEW) {
                if ( ! $assoc['isCascadePersist']) {
                    throw new InvalidArgumentException("A new entity was found through the relationship '"
                            . $assoc['sourceEntity'] . "#" . $assoc['fieldName'] . "' that was not"
                            . " configured to cascade persist operations for entity: " . self::objToStr($entry) . "."
                            . " Explicitly persist the new entity or configure cascading persist operations"
                            . " on the relationship. If you cannot find out which entity causes the problem"
                            . " implement '" . $assoc['targetEntity'] . "#__toString()' to get a clue.");
                }
                $this->persistNew($targetClass, $entry);
                $this->computeChangeSet($targetClass, $entry);
            } else if ($state == self::STATE_REMOVED) {
                return new InvalidArgumentException("Removed entity detected during flush: "
                        . self::objToStr($entry).". Remove deleted entities from associations.");
            } else if ($state == self::STATE_DETACHED) {
                // Can actually not happen right now as we assume STATE_NEW,
                // so the exception will be raised from the DBAL layer (constraint violation).
                throw new InvalidArgumentException("A detached entity was found through a "
                        . "relationship during cascading a persist operation.");
            }
            // MANAGED associated entities are already taken into account
            // during changeset calculation anyway, since they are in the identity map.
        }
    }

    private function persistNew($class, $entity)
    {
        $oid = spl_object_hash($entity);
        if (isset($class->lifecycleCallbacks[Events::prePersist])) {
            $class->invokeLifecycleCallbacks(Events::prePersist, $entity);
        }
        if ($this->evm->hasListeners(Events::prePersist)) {
            $this->evm->dispatchEvent(Events::prePersist, new LifecycleEventArgs($entity, $this->em));
        }

        $idGen = $class->idGenerator;
        if ( ! $idGen->isPostInsertGenerator()) {
            $idValue = $idGen->generate($this->em, $entity);
            if ( ! $idGen instanceof \Doctrine\ORM\Id\AssignedGenerator) {
                $this->entityIdentifiers[$oid] = array($class->identifier[0] => $idValue);
                $class->setIdentifierValues($entity, $this->entityIdentifiers[$oid]);
            } else {
                $this->entityIdentifiers[$oid] = $idValue;
            }
        }
        $this->entityStates[$oid] = self::STATE_MANAGED;

        $this->scheduleForInsert($entity);
    }
    
    /**
     * INTERNAL:
     * Computes the changeset of an individual entity, independently of the
     * computeChangeSets() routine that is used at the beginning of a UnitOfWork#commit().
     * 
     * The passed entity must be a managed entity. If the entity already has a change set
     * because this method is invoked during a commit cycle then the change sets are added.
     * whereby changes detected in this method prevail.
     * 
     * @ignore
     * @param ClassMetadata $class The class descriptor of the entity.
     * @param object $entity The entity for which to (re)calculate the change set.
     * @throws InvalidArgumentException If the passed entity is not MANAGED.
     */
    public function recomputeSingleEntityChangeSet($class, $entity)
    {
        $oid = spl_object_hash($entity);
        
        if ( ! isset($this->entityStates[$oid]) || $this->entityStates[$oid] != self::STATE_MANAGED) {
            throw new InvalidArgumentException('Entity must be managed.');
        }
        
        /* TODO: Just return if changetracking policy is NOTIFY?
        if ($class->isChangeTrackingNotify()) {
            return;
        }*/

        if ( ! $class->isInheritanceTypeNone()) {
            $class = $this->em->getClassMetadata(get_class($entity));
        }

        $actualData = array();
        foreach ($class->reflFields as $name => $refProp) {
            if ( ! $class->isIdentifier($name) || ! $class->isIdGeneratorIdentity()) {
                $actualData[$name] = $refProp->getValue($entity);
            }
        }

        $originalData = $this->originalEntityData[$oid];
        $changeSet = array();

        foreach ($actualData as $propName => $actualValue) {
            $orgValue = isset($originalData[$propName]) ? $originalData[$propName] : null;
            if (is_object($orgValue) && $orgValue !== $actualValue) {
                $changeSet[$propName] = array($orgValue, $actualValue);
            } else if ($orgValue != $actualValue || ($orgValue === null ^ $actualValue === null)) {
                $changeSet[$propName] = array($orgValue, $actualValue);
            }
        }

        if ($changeSet) {
            if (isset($this->entityChangeSets[$oid])) {
                $this->entityChangeSets[$oid] = array_merge($this->entityChangeSets[$oid], $changeSet);
            }
            $this->originalEntityData[$oid] = $actualData;
        }
    }

    /**
     * Executes all entity insertions for entities of the specified type.
     *
     * @param Doctrine\ORM\Mapping\ClassMetadata $class
     */
    private function executeInserts($class)
    {
        $className = $class->name;
        $persister = $this->getEntityPersister($className);
        
        $hasLifecycleCallbacks = isset($class->lifecycleCallbacks[Events::postPersist]);
        $hasListeners = $this->evm->hasListeners(Events::postPersist);
        if ($hasLifecycleCallbacks || $hasListeners) {
            $entities = array();
        }
        
        foreach ($this->entityInsertions as $oid => $entity) {
            if (get_class($entity) === $className) {
                $persister->addInsert($entity);
                unset($this->entityInsertions[$oid]);
                if ($hasLifecycleCallbacks || $hasListeners) {
                    $entities[] = $entity;
                }
            }
        }

        $postInsertIds = $persister->executeInserts();

        if ($postInsertIds) {
            // Persister returned post-insert IDs
            foreach ($postInsertIds as $id => $entity) {
                $oid = spl_object_hash($entity);
                $idField = $class->identifier[0];
                $class->reflFields[$idField]->setValue($entity, $id);
                $this->entityIdentifiers[$oid] = array($idField => $id);
                $this->entityStates[$oid] = self::STATE_MANAGED;
                $this->originalEntityData[$oid][$idField] = $id;
                $this->addToIdentityMap($entity);
            }
        }
        
        if ($hasLifecycleCallbacks || $hasListeners) {
            foreach ($entities as $entity) {
                if ($hasLifecycleCallbacks) {
                    $class->invokeLifecycleCallbacks(Events::postPersist, $entity);
                }
                if ($hasListeners) {
                    $this->evm->dispatchEvent(Events::postPersist, new LifecycleEventArgs($entity, $this->em));
                }
            }
        }
    }

    /**
     * Executes all entity updates for entities of the specified type.
     *
     * @param Doctrine\ORM\Mapping\ClassMetadata $class
     */
    private function executeUpdates($class)
    {
        $className = $class->name;
        $persister = $this->getEntityPersister($className);

        $hasPreUpdateLifecycleCallbacks = isset($class->lifecycleCallbacks[Events::preUpdate]);
        $hasPreUpdateListeners = $this->evm->hasListeners(Events::preUpdate);
        $hasPostUpdateLifecycleCallbacks = isset($class->lifecycleCallbacks[Events::postUpdate]);
        $hasPostUpdateListeners = $this->evm->hasListeners(Events::postUpdate);
        
        foreach ($this->entityUpdates as $oid => $entity) {
            if (get_class($entity) == $className || $entity instanceof Proxy && get_parent_class($entity) == $className) {
                
                if ($hasPreUpdateLifecycleCallbacks) {
                    $class->invokeLifecycleCallbacks(Events::preUpdate, $entity);
                    $this->recomputeSingleEntityChangeSet($class, $entity);
                }
                
                if ($hasPreUpdateListeners) {
                    $this->evm->dispatchEvent(Events::preUpdate, new Event\PreUpdateEventArgs(
                        $entity, $this->em, $this->entityChangeSets[$oid])
                    );
                }

                if ($this->entityChangeSets[$oid]) {
                    $persister->update($entity);
                }
                unset($this->entityUpdates[$oid]);
                
                if ($hasPostUpdateLifecycleCallbacks) {
                    $class->invokeLifecycleCallbacks(Events::postUpdate, $entity);
                }
                if ($hasPostUpdateListeners) {
                    $this->evm->dispatchEvent(Events::postUpdate, new LifecycleEventArgs($entity, $this->em));
                }
            }
        }
    }

    /**
     * Executes all entity deletions for entities of the specified type.
     *
     * @param Doctrine\ORM\Mapping\ClassMetadata $class
     */
    private function executeDeletions($class)
    {
        $className = $class->name;
        $persister = $this->getEntityPersister($className);
                
        $hasLifecycleCallbacks = isset($class->lifecycleCallbacks[Events::postRemove]);
        $hasListeners = $this->evm->hasListeners(Events::postRemove);
        
        foreach ($this->entityDeletions as $oid => $entity) {
            if (get_class($entity) == $className || $entity instanceof Proxy && get_parent_class($entity) == $className) {
                $persister->delete($entity);
                unset(
                    $this->entityDeletions[$oid],
                    $this->entityIdentifiers[$oid],
                    $this->originalEntityData[$oid],
                    $this->entityStates[$oid]
                    );
                // Entity with this $oid after deletion treated as NEW, even if the $oid
                // is obtained by a new entity because the old one went out of scope.
                //$this->entityStates[$oid] = self::STATE_NEW;
                if ( ! $class->isIdentifierNatural()) {
                    $class->reflFields[$class->identifier[0]]->setValue($entity, null);
                }

                if ($hasLifecycleCallbacks) {
                    $class->invokeLifecycleCallbacks(Events::postRemove, $entity);
                }
                if ($hasListeners) {
                    $this->evm->dispatchEvent(Events::postRemove, new LifecycleEventArgs($entity, $this->em));
                }
            }
        }
    }

    /**
     * Gets the commit order.
     *
     * @return array
     */
    private function getCommitOrder(array $entityChangeSet = null)
    {
        if ($entityChangeSet === null) {
            $entityChangeSet = array_merge(
                    $this->entityInsertions,
                    $this->entityUpdates,
                    $this->entityDeletions
                    );
        }
        
        $calc = $this->getCommitOrderCalculator();
        
        // See if there are any new classes in the changeset, that are not in the
        // commit order graph yet (dont have a node).
        $newNodes = array();
        foreach ($entityChangeSet as $oid => $entity) {
            $className = get_class($entity);         
            if ( ! $calc->hasClass($className)) {
                $class = $this->em->getClassMetadata($className);
                $calc->addClass($class);
                $newNodes[] = $class;
            }
        }

        // Calculate dependencies for new nodes
        foreach ($newNodes as $class) {
            foreach ($class->associationMappings as $assoc) {
                if ($assoc['isOwningSide'] && $assoc['type'] & ClassMetadata::TO_ONE) {
                    $targetClass = $this->em->getClassMetadata($assoc['targetEntity']);
                    if ( ! $calc->hasClass($targetClass->name)) {
                        $calc->addClass($targetClass);
                    }
                    $calc->addDependency($targetClass, $class);
                    // If the target class has mapped subclasses,
                    // these share the same dependency.
                    if ($targetClass->subClasses) {
                        foreach ($targetClass->subClasses as $subClassName) {
                            $targetSubClass = $this->em->getClassMetadata($subClassName);
                            if ( ! $calc->hasClass($subClassName)) {
                                $calc->addClass($targetSubClass);
                            }
                            $calc->addDependency($targetSubClass, $class);
                        }
                    }
                }
            }
        }

        return $calc->getCommitOrder();
    }

    /**
     * Schedules an entity for insertion into the database.
     * If the entity already has an identifier, it will be added to the identity map.
     *
     * @param object $entity The entity to schedule for insertion.
     */
    public function scheduleForInsert($entity)
    {
        $oid = spl_object_hash($entity);

        if (isset($this->entityUpdates[$oid])) {
            throw new InvalidArgumentException("Dirty entity can not be scheduled for insertion.");
        }
        if (isset($this->entityDeletions[$oid])) {
            throw new InvalidArgumentException("Removed entity can not be scheduled for insertion.");
        }
        if (isset($this->entityInsertions[$oid])) {
            throw new InvalidArgumentException("Entity can not be scheduled for insertion twice.");
        }

        $this->entityInsertions[$oid] = $entity;

        if (isset($this->entityIdentifiers[$oid])) {
            $this->addToIdentityMap($entity);
        }
    }

    /**
     * Checks whether an entity is scheduled for insertion.
     *
     * @param object $entity
     * @return boolean
     */
    public function isScheduledForInsert($entity)
    {
        return isset($this->entityInsertions[spl_object_hash($entity)]);
    }

    /**
     * Schedules an entity for being updated.
     *
     * @param object $entity The entity to schedule for being updated.
     */
    public function scheduleForUpdate($entity)
    {
        $oid = spl_object_hash($entity);
        if ( ! isset($this->entityIdentifiers[$oid])) {
            throw new InvalidArgumentException("Entity has no identity.");
        }
        if (isset($this->entityDeletions[$oid])) {
            throw new InvalidArgumentException("Entity is removed.");
        }

        if ( ! isset($this->entityUpdates[$oid]) && ! isset($this->entityInsertions[$oid])) {
            $this->entityUpdates[$oid] = $entity;
        }
    }
    
    /**
     * INTERNAL:
     * Schedules an extra update that will be executed immediately after the
     * regular entity updates within the currently running commit cycle.
     * 
     * Extra updates for entities are stored as (entity, changeset) tuples.
     * 
     * @ignore
     * @param object $entity The entity for which to schedule an extra update.
     * @param array $changeset The changeset of the entity (what to update).
     */
    public function scheduleExtraUpdate($entity, array $changeset)
    {
        $oid = spl_object_hash($entity);
        if (isset($this->extraUpdates[$oid])) {
            list($ignored, $changeset2) = $this->extraUpdates[$oid];
            $this->extraUpdates[$oid] = array($entity, $changeset + $changeset2);
        } else {
            $this->extraUpdates[$oid] = array($entity, $changeset);
        }
    }

    /**
     * Checks whether an entity is registered as dirty in the unit of work.
     * Note: Is not very useful currently as dirty entities are only registered
     * at commit time.
     *
     * @param object $entity
     * @return boolean
     */
    public function isScheduledForUpdate($entity)
    {
        return isset($this->entityUpdates[spl_object_hash($entity)]);
    }

    public function isScheduledForDirtyCheck($entity)
    {
        $rootEntityName = $this->em->getClassMetadata(get_class($entity))->rootEntityName;
        return isset($this->scheduledForDirtyCheck[$rootEntityName][spl_object_hash($entity)]);
    }

    /**
     * INTERNAL:
     * Schedules an entity for deletion.
     * 
     * @param object $entity
     */
    public function scheduleForDelete($entity)
    {
        $oid = spl_object_hash($entity);
        
        if (isset($this->entityInsertions[$oid])) {
            if ($this->isInIdentityMap($entity)) {
                $this->removeFromIdentityMap($entity);
            }
            unset($this->entityInsertions[$oid], $this->entityStates[$oid]);
            return; // entity has not been persisted yet, so nothing more to do.
        }

        if ( ! $this->isInIdentityMap($entity)) {
            return; // ignore
        }

        $this->removeFromIdentityMap($entity);

        if (isset($this->entityUpdates[$oid])) {
            unset($this->entityUpdates[$oid]);
        }
        if ( ! isset($this->entityDeletions[$oid])) {
            $this->entityDeletions[$oid] = $entity;
            $this->entityStates[$oid] = self::STATE_REMOVED;
        }
    }

    /**
     * Checks whether an entity is registered as removed/deleted with the unit
     * of work.
     *
     * @param object $entity
     * @return boolean
     */
    public function isScheduledForDelete($entity)
    {
        return isset($this->entityDeletions[spl_object_hash($entity)]);
    }

    /**
     * Checks whether an entity is scheduled for insertion, update or deletion.
     * 
     * @param $entity
     * @return boolean
     */
    public function isEntityScheduled($entity)
    {
        $oid = spl_object_hash($entity);
        return isset($this->entityInsertions[$oid]) ||
                isset($this->entityUpdates[$oid]) ||
                isset($this->entityDeletions[$oid]);
    }

    /**
     * INTERNAL:
     * Registers an entity in the identity map.
     * Note that entities in a hierarchy are registered with the class name of
     * the root entity.
     *
     * @ignore
     * @param object $entity  The entity to register.
     * @return boolean  TRUE if the registration was successful, FALSE if the identity of
     *                  the entity in question is already managed.
     */
    public function addToIdentityMap($entity)
    {
        $classMetadata = $this->em->getClassMetadata(get_class($entity));
        $idHash = implode(' ', $this->entityIdentifiers[spl_object_hash($entity)]);
        if ($idHash === '') {
            throw new InvalidArgumentException("The given entity has no identity.");
        }
        $className = $classMetadata->rootEntityName;
        if (isset($this->identityMap[$className][$idHash])) {
            return false;
        }
        $this->identityMap[$className][$idHash] = $entity;
        if ($entity instanceof NotifyPropertyChanged) {
            $entity->addPropertyChangedListener($this);
        }
        return true;
    }

    /**
     * Gets the state of an entity with regard to the current unit of work.
     *
     * @param object $entity
     * @param integer $assume The state to assume if the state is not yet known (not MANAGED or REMOVED).
     *                        This parameter can be set to improve performance of entity state detection
     *                        by potentially avoiding a database lookup if the distinction between NEW and DETACHED
     *                        is either known or does not matter for the caller of the method.
     * @return int The entity state.
     */
    public function getEntityState($entity, $assume = null)
    {
        $oid = spl_object_hash($entity);
        if ( ! isset($this->entityStates[$oid])) {
            // State can only be NEW or DETACHED, because MANAGED/REMOVED states are known.
            // Note that you can not remember the NEW or DETACHED state in _entityStates since
            // the UoW does not hold references to such objects and the object hash can be reused.
            // More generally because the state may "change" between NEW/DETACHED without the UoW being aware of it.
            if ($assume === null) {
                $class = $this->em->getClassMetadata(get_class($entity));
                $id = $class->getIdentifierValues($entity);
                if ( ! $id) {
                    return self::STATE_NEW;
                } else if ($class->isIdentifierNatural()) {
                    // Check for a version field, if available, to avoid a db lookup.
                    if ($class->isVersioned) {
                        if ($class->getFieldValue($entity, $class->versionField)) {
                            return self::STATE_DETACHED;
                        } else {
                            return self::STATE_NEW;
                        }
                    } else {
                        // Last try before db lookup: check the identity map.
                        if ($this->tryGetById($id, $class->rootEntityName)) {
                            return self::STATE_DETACHED;
                        } else {
                            // db lookup
                            if ($this->getEntityPersister(get_class($entity))->exists($entity)) {
                                return self::STATE_DETACHED;
                            } else {
                                return self::STATE_NEW;
                            }
                        }
                    }
                } else {
                    return self::STATE_DETACHED;
                }
            } else {
                return $assume;
            }
        }
        return $this->entityStates[$oid];
    }

    /**
     * INTERNAL:
     * Removes an entity from the identity map. This effectively detaches the
     * entity from the persistence management of Doctrine.
     *
     * @ignore
     * @param object $entity
     * @return boolean
     */
    public function removeFromIdentityMap($entity)
    {
        $oid = spl_object_hash($entity);
        $classMetadata = $this->em->getClassMetadata(get_class($entity));
        $idHash = implode(' ', $this->entityIdentifiers[$oid]);
        if ($idHash === '') {
            throw new InvalidArgumentException("The given entity has no identity.");
        }
        $className = $classMetadata->rootEntityName;
        if (isset($this->identityMap[$className][$idHash])) {
            unset($this->identityMap[$className][$idHash]);
            //$this->entityStates[$oid] = self::STATE_DETACHED;
            return true;
        }

        return false;
    }

    /**
     * INTERNAL:
     * Gets an entity in the identity map by its identifier hash.
     *
     * @ignore
     * @param string $idHash
     * @param string $rootClassName
     * @return object
     */
    public function getByIdHash($idHash, $rootClassName)
    {
        return $this->identityMap[$rootClassName][$idHash];
    }

    /**
     * INTERNAL:
     * Tries to get an entity by its identifier hash. If no entity is found for
     * the given hash, FALSE is returned.
     *
     * @ignore
     * @param string $idHash
     * @param string $rootClassName
     * @return mixed The found entity or FALSE.
     */
    public function tryGetByIdHash($idHash, $rootClassName)
    {
        return isset($this->identityMap[$rootClassName][$idHash]) ?
                $this->identityMap[$rootClassName][$idHash] : false;
    }

    /**
     * Checks whether an entity is registered in the identity map of this UnitOfWork.
     *
     * @param object $entity
     * @return boolean
     */
    public function isInIdentityMap($entity)
    {
        $oid = spl_object_hash($entity);
        if ( ! isset($this->entityIdentifiers[$oid])) {
            return false;
        }
        $classMetadata = $this->em->getClassMetadata(get_class($entity));
        $idHash = implode(' ', $this->entityIdentifiers[$oid]);
        if ($idHash === '') {
            return false;
        }
        
        return isset($this->identityMap[$classMetadata->rootEntityName][$idHash]);
    }

    /**
     * INTERNAL:
     * Checks whether an identifier hash exists in the identity map.
     *
     * @ignore
     * @param string $idHash
     * @param string $rootClassName
     * @return boolean
     */
    public function containsIdHash($idHash, $rootClassName)
    {
        return isset($this->identityMap[$rootClassName][$idHash]);
    }

    /**
     * Persists an entity as part of the current unit of work.
     *
     * @param object $entity The entity to persist.
     */
    public function persist($entity)
    {
        $visited = array();
        $this->doPersist($entity, $visited);
    }

    /**
     * Persists an entity as part of the current unit of work.
     * 
     * This method is internally called during persist() cascades as it tracks
     * the already visited entities to prevent infinite recursions.
     *
     * @param object $entity The entity to persist.
     * @param array $visited The already visited entities.
     */
    private function doPersist($entity, array &$visited)
    {
        $oid = spl_object_hash($entity);
        if (isset($visited[$oid])) {
            return; // Prevent infinite recursion
        }

        $visited[$oid] = $entity; // Mark visited

        $class = $this->em->getClassMetadata(get_class($entity));

        // We assume NEW, so DETACHED entities result in an exception on flush (constraint violation).
        // If we would detect DETACHED here we would throw an exception anyway with the same
        // consequences (not recoverable/programming error), so just assuming NEW here
        // lets us avoid some database lookups for entities with natural identifiers.
        $entityState = $this->getEntityState($entity, self::STATE_NEW);

        switch ($entityState) {
            case self::STATE_MANAGED:
                // Nothing to do, except if policy is "deferred explicit"
                if ($class->isChangeTrackingDeferredExplicit()) {
                    $this->scheduleForDirtyCheck($entity);
                }
                break;
            case self::STATE_NEW:
                $this->persistNew($class, $entity);
                break;
            case self::STATE_REMOVED:
                // Entity becomes managed again
                unset($this->entityDeletions[$oid]);
                $this->entityStates[$oid] = self::STATE_MANAGED;
                break;
            case self::STATE_DETACHED:
                // Can actually not happen right now since we assume STATE_NEW.
                throw new InvalidArgumentException("Detached entity passed to persist().");
            default:
                throw new UnexpectedValueException("Unexpected entity state: $entityState.");
        }

        $this->cascadePersist($entity, $visited);
    }

    /**
     * Deletes an entity as part of the current unit of work.
     *
     * @param object $entity The entity to remove.
     */
    public function remove($entity)
    {
        $visited = array();
        $this->doRemove($entity, $visited);
    }

    /**
     * Deletes an entity as part of the current unit of work.
     *
     * This method is internally called during delete() cascades as it tracks
     * the already visited entities to prevent infinite recursions.
     *
     * @param object $entity The entity to delete.
     * @param array $visited The map of the already visited entities.
     * @throws InvalidArgumentException If the instance is a detached entity.
     */
    private function doRemove($entity, array &$visited)
    {
        $oid = spl_object_hash($entity);
        if (isset($visited[$oid])) {
            return; // Prevent infinite recursion
        }

        $visited[$oid] = $entity; // mark visited
        
        // Cascade first, because scheduleForDelete() removes the entity from the identity map, which 
        // can cause problems when a lazy proxy has to be initialized for the cascade operation.
        $this->cascadeRemove($entity, $visited);

        $class = $this->em->getClassMetadata(get_class($entity));
        $entityState = $this->getEntityState($entity);
        switch ($entityState) {
            case self::STATE_NEW:
            case self::STATE_REMOVED:
                // nothing to do
                break;
            case self::STATE_MANAGED:
                if (isset($class->lifecycleCallbacks[Events::preRemove])) {
                    $class->invokeLifecycleCallbacks(Events::preRemove, $entity);
                }
                if ($this->evm->hasListeners(Events::preRemove)) {
                    $this->evm->dispatchEvent(Events::preRemove, new LifecycleEventArgs($entity, $this->em));
                }
                $this->scheduleForDelete($entity);
                break;
            case self::STATE_DETACHED:
                throw new InvalidArgumentException("A detached entity can not be removed.");
            default:
                throw new UnexpectedValueException("Unexpected entity state: $entityState.");
        }

    }

    /**
     * Merges the state of the given detached entity into this UnitOfWork.
     *
     * @param object $entity
     * @return object The managed copy of the entity.
     * @throws OptimisticLockException If the entity uses optimistic locking through a version
     *         attribute and the version check against the managed copy fails.
     *
     * @todo Require active transaction!? OptimisticLockException may result in undefined state!?
     */
    public function merge($entity)
    {
        $visited = array();
        return $this->doMerge($entity, $visited);
    }

    /**
     * Executes a merge operation on an entity.
     *
     * @param object $entity
     * @param array $visited
     * @return object The managed copy of the entity.
     * @throws OptimisticLockException If the entity uses optimistic locking through a version
     *         attribute and the version check against the managed copy fails.
     * @throws InvalidArgumentException If the entity instance is NEW.
     */
    private function doMerge($entity, array &$visited, $prevManagedCopy = null, $assoc = null)
    {
        $oid = spl_object_hash($entity);
        if (isset($visited[$oid])) {
            return; // Prevent infinite recursion
        }

        $visited[$oid] = $entity; // mark visited

        $class = $this->em->getClassMetadata(get_class($entity));

        // First we assume DETACHED, although it can still be NEW but we can avoid
        // an extra db-roundtrip this way. If it is not MANAGED but has an identity,
        // we need to fetch it from the db anyway in order to merge.
        // MANAGED entities are ignored by the merge operation.
        if ($this->getEntityState($entity, self::STATE_DETACHED) == self::STATE_MANAGED) {
            $managedCopy = $entity;
        } else {
            // Try to look the entity up in the identity map.
            $id = $class->getIdentifierValues($entity);

            // If there is no ID, it is actually NEW.
            if ( ! $id) {
                $managedCopy = $class->newInstance();
                $this->persistNew($class, $managedCopy);
            } else {
                $managedCopy = $this->tryGetById($id, $class->rootEntityName);
                if ($managedCopy) {
                    // We have the entity in-memory already, just make sure its not removed.
                    if ($this->getEntityState($managedCopy) == self::STATE_REMOVED) {
                        throw new InvalidArgumentException('Removed entity detected during merge.'
                                . ' Can not merge with a removed entity.');
                    }
                } else {
                    // We need to fetch the managed copy in order to merge.
                    $managedCopy = $this->em->find($class->name, $id);
                }

                if ($managedCopy === null) {
                    // If the identifier is ASSIGNED, it is NEW, otherwise an error
                    // since the managed entity was not found.
                    if ($class->isIdentifierNatural()) {
                        $managedCopy = $class->newInstance();
                        $class->setIdentifierValues($managedCopy, $id);
                        $this->persistNew($class, $managedCopy);
                    } else {
                        throw new EntityNotFoundException;
                    }
                }
            }

            if ($class->isVersioned) {
                $managedCopyVersion = $class->reflFields[$class->versionField]->getValue($managedCopy);
                $entityVersion = $class->reflFields[$class->versionField]->getValue($entity);
                // Throw exception if versions dont match.
                if ($managedCopyVersion != $entityVersion) {
                    throw OptimisticLockException::lockFailedVersionMissmatch($entityVersion, $managedCopyVersion);
                }
            }

            // Merge state of $entity into existing (managed) entity
            foreach ($class->reflFields as $name => $prop) {
                if ( ! isset($class->associationMappings[$name])) {
                    if ( ! $class->isIdentifier($name)) {
                        $prop->setValue($managedCopy, $prop->getValue($entity));
                    }
                } else {
                    $assoc2 = $class->associationMappings[$name];
                    if ($assoc2['type'] & ClassMetadata::TO_ONE) {
                        $other = $prop->getValue($entity);
                        if ($other === null) {
                            $prop->setValue($managedCopy, null);
                        } else if ($other instanceof Proxy && !$other->__isInitialized__) {
                            // do not merge fields marked lazy that have not been fetched.
                            continue;
                        } else if ( ! $assoc2['isCascadeMerge']) {
                            if ($this->getEntityState($other, self::STATE_DETACHED) == self::STATE_MANAGED) {
                                $prop->setValue($managedCopy, $other);
                            } else {
                                $targetClass = $this->em->getClassMetadata($assoc2['targetEntity']);
                                $id = $targetClass->getIdentifierValues($other);
                                $proxy = $this->em->getProxyFactory()->getProxy($assoc2['targetEntity'], $id);
                                $prop->setValue($managedCopy, $proxy);
                                $this->registerManaged($proxy, $id, array());
                            }
                        }
                    } else {
                        $mergeCol = $prop->getValue($entity);
                        if ($mergeCol instanceof PersistentCollection && !$mergeCol->isInitialized()) {
                            // do not merge fields marked lazy that have not been fetched.
                            // keep the lazy persistent collection of the managed copy.
                            continue;
                        }

                        $managedCol = $prop->getValue($managedCopy);
                        if (!$managedCol) {
                            $managedCol = new PersistentCollection($this->em,
                                    $this->em->getClassMetadata($assoc2['targetEntity']),
                                    new ArrayCollection
                                    );
                            $managedCol->setOwner($managedCopy, $assoc2);
                            $prop->setValue($managedCopy, $managedCol);
                            $this->originalEntityData[$oid][$name] = $managedCol;
                        }
                        if ($assoc2['isCascadeMerge']) {
                            $managedCol->initialize();
                            if (!$managedCol->isEmpty()) {
                                $managedCol->unwrap()->clear();
                                $managedCol->setDirty(true);
                                if ($assoc2['isOwningSide'] && $assoc2['type'] == ClassMetadata::MANY_TO_MANY && $class->isChangeTrackingNotify()) {
                                    $this->scheduleForDirtyCheck($managedCopy);
                                }
                            }
                        }
                    }
                }
                if ($class->isChangeTrackingNotify()) {
                    // Just treat all properties as changed, there is no other choice.
                    $this->propertyChanged($managedCopy, $name, null, $prop->getValue($managedCopy));
                }
            }
            if ($class->isChangeTrackingDeferredExplicit()) {
                $this->scheduleForDirtyCheck($entity);
            }
        }

        if ($prevManagedCopy !== null) {
            $assocField = $assoc['fieldName'];
            $prevClass = $this->em->getClassMetadata(get_class($prevManagedCopy));
            if ($assoc['type'] & ClassMetadata::TO_ONE) {
                $prevClass->reflFields[$assocField]->setValue($prevManagedCopy, $managedCopy);
            } else {
                $prevClass->reflFields[$assocField]->getValue($prevManagedCopy)->add($managedCopy);
                if ($assoc['type'] == ClassMetadata::ONE_TO_MANY) {
                    $class->reflFields[$assoc['mappedBy']]->setValue($managedCopy, $prevManagedCopy);
                }
            }
        }

        // Mark the managed copy visited as well
        $visited[spl_object_hash($managedCopy)] = true;

        $this->cascadeMerge($entity, $managedCopy, $visited);

        return $managedCopy;
    }
    
    /**
     * Detaches an entity from the persistence management. It's persistence will
     * no longer be managed by Doctrine.
     *
     * @param object $entity The entity to detach.
     */
    public function detach($entity)
    {
        $visited = array();
        $this->doDetach($entity, $visited);
    }
    
    /**
     * Executes a detach operation on the given entity.
     * 
     * @param object $entity
     * @param array $visited
     */
    private function doDetach($entity, array &$visited)
    {
        $oid = spl_object_hash($entity);
        if (isset($visited[$oid])) {
            return; // Prevent infinite recursion
        }

        $visited[$oid] = $entity; // mark visited
        
        switch ($this->getEntityState($entity, self::STATE_DETACHED)) {
            case self::STATE_MANAGED:
                if ($this->isInIdentityMap($entity)) {
                    $this->removeFromIdentityMap($entity);
                }
                unset($this->entityInsertions[$oid], $this->entityUpdates[$oid],
                        $this->entityDeletions[$oid], $this->entityIdentifiers[$oid],
                        $this->entityStates[$oid], $this->originalEntityData[$oid]);
                break;
            case self::STATE_NEW:
            case self::STATE_DETACHED:
                return;
        }
        
        $this->cascadeDetach($entity, $visited);
    }
    
    /**
     * Refreshes the state of the given entity from the database, overwriting
     * any local, unpersisted changes.
     * 
     * @param object $entity The entity to refresh.
     * @throws InvalidArgumentException If the entity is not MANAGED.
     */
    public function refresh($entity)
    {
        $visited = array();
        $this->doRefresh($entity, $visited);
    }
    
    /**
     * Executes a refresh operation on an entity.
     * 
     * @param object $entity The entity to refresh.
     * @param array $visited The already visited entities during cascades.
     * @throws InvalidArgumentException If the entity is not MANAGED.
     */
    private function doRefresh($entity, array &$visited)
    {
        $oid = spl_object_hash($entity);
        if (isset($visited[$oid])) {
            return; // Prevent infinite recursion
        }

        $visited[$oid] = $entity; // mark visited

        $class = $this->em->getClassMetadata(get_class($entity));
        if ($this->getEntityState($entity) == self::STATE_MANAGED) {
            $this->getEntityPersister($class->name)->refresh(
                array_combine($class->getIdentifierFieldNames(), $this->entityIdentifiers[$oid]),
                $entity
            );
        } else {
            throw new InvalidArgumentException("Entity is not MANAGED.");
        }
        
        $this->cascadeRefresh($entity, $visited);
    }
    
    /**
     * Cascades a refresh operation to associated entities.
     *
     * @param object $entity
     * @param array $visited
     */
    private function cascadeRefresh($entity, array &$visited)
    {
        $class = $this->em->getClassMetadata(get_class($entity));
        foreach ($class->associationMappings as $assoc) {
            if ( ! $assoc['isCascadeRefresh']) {
                continue;
            }
            $relatedEntities = $class->reflFields[$assoc['fieldName']]->getValue($entity);
            if ($relatedEntities instanceof Collection) {
                if ($relatedEntities instanceof PersistentCollection) {
                    // Unwrap so that foreach() does not initialize
                    $relatedEntities = $relatedEntities->unwrap();
                }
                foreach ($relatedEntities as $relatedEntity) {
                    $this->doRefresh($relatedEntity, $visited);
                }
            } else if ($relatedEntities !== null) {
                $this->doRefresh($relatedEntities, $visited);
            }
        }
    }
    
    /**
     * Cascades a detach operation to associated entities.
     *
     * @param object $entity
     * @param array $visited
     */
    private function cascadeDetach($entity, array &$visited)
    {
        $class = $this->em->getClassMetadata(get_class($entity));
        foreach ($class->associationMappings as $assoc) {
            if ( ! $assoc['isCascadeDetach']) {
                continue;
            }
            $relatedEntities = $class->reflFields[$assoc['fieldName']]->getValue($entity);
            if ($relatedEntities instanceof Collection) {
                if ($relatedEntities instanceof PersistentCollection) {
                    // Unwrap so that foreach() does not initialize
                    $relatedEntities = $relatedEntities->unwrap();
                }
                foreach ($relatedEntities as $relatedEntity) {
                    $this->doDetach($relatedEntity, $visited);
                }
            } else if ($relatedEntities !== null) {
                $this->doDetach($relatedEntities, $visited);
            }
        }
    }

    /**
     * Cascades a merge operation to associated entities.
     *
     * @param object $entity
     * @param object $managedCopy
     * @param array $visited
     */
    private function cascadeMerge($entity, $managedCopy, array &$visited)
    {
        $class = $this->em->getClassMetadata(get_class($entity));
        foreach ($class->associationMappings as $assoc) {
            if ( ! $assoc['isCascadeMerge']) {
                continue;
            }
            $relatedEntities = $class->reflFields[$assoc['fieldName']]->getValue($entity);
            if ($relatedEntities instanceof Collection) {
                if ($relatedEntities instanceof PersistentCollection) {
                    // Unwrap so that foreach() does not initialize
                    $relatedEntities = $relatedEntities->unwrap();
                }
                foreach ($relatedEntities as $relatedEntity) {
                    $this->doMerge($relatedEntity, $visited, $managedCopy, $assoc);
                }
            } else if ($relatedEntities !== null) {
                $this->doMerge($relatedEntities, $visited, $managedCopy, $assoc);
            }
        }
    }

    /**
     * Cascades the save operation to associated entities.
     *
     * @param object $entity
     * @param array $visited
     * @param array $insertNow
     */
    private function cascadePersist($entity, array &$visited)
    {
        $class = $this->em->getClassMetadata(get_class($entity));
        foreach ($class->associationMappings as $assoc) {
            if ( ! $assoc['isCascadePersist']) {
                continue;
            }
            
            $relatedEntities = $class->reflFields[$assoc['fieldName']]->getValue($entity);
            if (($relatedEntities instanceof Collection || is_array($relatedEntities))) {
                if ($relatedEntities instanceof PersistentCollection) {
                    // Unwrap so that foreach() does not initialize
                    $relatedEntities = $relatedEntities->unwrap();
                }
                foreach ($relatedEntities as $relatedEntity) {
                    $this->doPersist($relatedEntity, $visited);
                }
            } else if ($relatedEntities !== null) {
                $this->doPersist($relatedEntities, $visited);
            }
        }
    }

    /**
     * Cascades the delete operation to associated entities.
     *
     * @param object $entity
     * @param array $visited
     */
    private function cascadeRemove($entity, array &$visited)
    {
        $class = $this->em->getClassMetadata(get_class($entity));
        foreach ($class->associationMappings as $assoc) {
            if ( ! $assoc['isCascadeRemove']) {
                continue;
            }
            
            if ($entity instanceof Proxy && !$entity->__isInitialized__) {
                $entity->__load();
            }
            
            $relatedEntities = $class->reflFields[$assoc['fieldName']]->getValue($entity);
            if ($relatedEntities instanceof Collection || is_array($relatedEntities)) {
                // If its a PersistentCollection initialization is intended! No unwrap!
                foreach ($relatedEntities as $relatedEntity) {
                    $this->doRemove($relatedEntity, $visited);
                }
            } else if ($relatedEntities !== null) {
                $this->doRemove($relatedEntities, $visited);
            }
        }
    }

    /**
     * Acquire a lock on the given entity.
     *
     * @param object $entity
     * @param int $lockMode
     * @param int $lockVersion
     */
    public function lock($entity, $lockMode, $lockVersion = null)
    {
        if ($this->getEntityState($entity) != self::STATE_MANAGED) {
            throw new InvalidArgumentException("Entity is not MANAGED.");
        }
        
        $entityName = get_class($entity);
        $class = $this->em->getClassMetadata($entityName);

        if ($lockMode == \Doctrine\DBAL\LockMode::OPTIMISTIC) {
            if (!$class->isVersioned) {
                throw OptimisticLockException::notVersioned($entityName);
            }

            if ($lockVersion != null) {
                $entityVersion = $class->reflFields[$class->versionField]->getValue($entity);
                if ($entityVersion != $lockVersion) {
                    throw OptimisticLockException::lockFailedVersionMissmatch($entity, $lockVersion, $entityVersion);
                }
            }
        } else if (in_array($lockMode, array(\Doctrine\DBAL\LockMode::PESSIMISTIC_READ, \Doctrine\DBAL\LockMode::PESSIMISTIC_WRITE))) {

            if (!$this->em->getConnection()->isTransactionActive()) {
                throw TransactionRequiredException::transactionRequired();
            }
            
            $oid = spl_object_hash($entity);

            $this->getEntityPersister($class->name)->lock(
                array_combine($class->getIdentifierFieldNames(), $this->entityIdentifiers[$oid]),
                $lockMode
            );
        }
    }

    /**
     * Gets the CommitOrderCalculator used by the UnitOfWork to order commits.
     *
     * @return Doctrine\ORM\Internal\CommitOrderCalculator
     */
    public function getCommitOrderCalculator()
    {
        if ($this->commitOrderCalculator === null) {
            $this->commitOrderCalculator = new Internal\CommitOrderCalculator;
        }
        return $this->commitOrderCalculator;
    }

    /**
     * Clears the UnitOfWork.
     */
    public function clear()
    {
        $this->identityMap =
        $this->entityIdentifiers =
        $this->originalEntityData =
        $this->entityChangeSets =
        $this->entityStates =
        $this->scheduledForDirtyCheck =
        $this->entityInsertions =
        $this->entityUpdates =
        $this->entityDeletions =
        $this->collectionDeletions =
        $this->collectionUpdates =
        $this->extraUpdates =
        $this->orphanRemovals = array();
        if ($this->commitOrderCalculator !== null) {
            $this->commitOrderCalculator->clear();
        }

        if ($this->evm->hasListeners(Events::onClear)) {
            $this->evm->dispatchEvent(Events::onClear, new Event\OnClearEventArgs($this->em));
        }
    }
    
    /**
     * INTERNAL:
     * Schedules an orphaned entity for removal. The remove() operation will be
     * invoked on that entity at the beginning of the next commit of this
     * UnitOfWork.
     * 
     * @ignore
     * @param object $entity
     */
    public function scheduleOrphanRemoval($entity)
    {
        $this->orphanRemovals[spl_object_hash($entity)] = $entity;
    }
    
    /**
     * INTERNAL:
     * Schedules a complete collection for removal when this UnitOfWork commits.
     *
     * @param PersistentCollection $coll
     */
    public function scheduleCollectionDeletion(PersistentCollection $coll)
    {
        //TODO: if $coll is already scheduled for recreation ... what to do?
        // Just remove $coll from the scheduled recreations?
        $this->collectionDeletions[] = $coll;
    }

    public function isCollectionScheduledForDeletion(PersistentCollection $coll)
    {
        return in_array($coll, $this->collectionsDeletions, true);
    }

    /**
     * INTERNAL:
     * Creates an entity. Used for reconstitution of persistent entities.
     *
     * @ignore
     * @param string $className The name of the entity class.
     * @param array $data The data for the entity.
     * @param array $hints Any hints to account for during reconstitution/lookup of the entity.
     * @return object The managed entity instance.
     * @internal Highly performance-sensitive method.
     * 
     * @todo Rename: getOrCreateEntity
     */
    public function createEntity($className, array $data, &$hints = array())
    {
        $class = $this->em->getClassMetadata($className);
        //$isReadOnly = isset($hints[Query::HINT_READ_ONLY]);

        if ($class->isIdentifierComposite) {
            $id = array();
            foreach ($class->identifier as $fieldName) {
                if (isset($class->associationMappings[$fieldName])) {
                    $id[$fieldName] = $data[$class->associationMappings[$fieldName]['joinColumns'][0]['name']];
                } else {
                    $id[$fieldName] = $data[$fieldName];
                }
            }
            $idHash = implode(' ', $id);
        } else {
            if (isset($class->associationMappings[$class->identifier[0]])) {
                $idHash = $data[$class->associationMappings[$class->identifier[0]]['joinColumns'][0]['name']];
            } else {
                $idHash = $data[$class->identifier[0]];
            }
            $id = array($class->identifier[0] => $idHash);
        }
        
        if (isset($this->identityMap[$class->rootEntityName][$idHash])) {            
            $entity = $this->identityMap[$class->rootEntityName][$idHash];
            $oid = spl_object_hash($entity);
            if ($entity instanceof Proxy && ! $entity->__isInitialized__) {
                $entity->__isInitialized__ = true;
                $overrideLocalValues = true;
                if ($entity instanceof NotifyPropertyChanged) {
                    $entity->addPropertyChangedListener($this);
                }
            } else {
                $overrideLocalValues = isset($hints[Query::HINT_REFRESH]);
            }

            if ($overrideLocalValues) {
                $this->originalEntityData[$oid] = $data;
            }
        } else {
            $entity = $class->newInstance();
            $oid = spl_object_hash($entity);
            $this->entityIdentifiers[$oid] = $id;
            $this->entityStates[$oid] = self::STATE_MANAGED;
            $this->originalEntityData[$oid] = $data;
            $this->identityMap[$class->rootEntityName][$idHash] = $entity;
            if ($entity instanceof NotifyPropertyChanged) {
                $entity->addPropertyChangedListener($this);
            }
            $overrideLocalValues = true;
        }

        if ($overrideLocalValues) {
            foreach ($data as $field => $value) {
                if (isset($class->fieldMappings[$field])) {
                    $class->reflFields[$field]->setValue($entity, $value);
                }
            }

            // Loading the entity right here, if its in the eager loading map get rid of it there.
            unset($this->eagerLoadingEntities[$class->rootEntityName][$idHash]);
            
            // Properly initialize any unfetched associations, if partial objects are not allowed.
            if ( ! isset($hints[Query::HINT_FORCE_PARTIAL_LOAD])) {
                foreach ($class->associationMappings as $field => $assoc) {
                    // Check if the association is not among the fetch-joined associations already.
                    if (isset($hints['fetched'][$className][$field])) {
                        continue;
                    }

                    $targetClass = $this->em->getClassMetadata($assoc['targetEntity']);

                    if ($assoc['type'] & ClassMetadata::TO_ONE) {
                        if ($assoc['isOwningSide']) {
                            $associatedId = array();
                            // TODO: Is this even computed right in all cases of composite keys?
                            foreach ($assoc['targetToSourceKeyColumns'] as $targetColumn => $srcColumn) {
                                $joinColumnValue = isset($data[$srcColumn]) ? $data[$srcColumn] : null;
                                if ($joinColumnValue !== null) {
                                    if ($targetClass->containsForeignIdentifier) {
                                        $associatedId[$targetClass->getFieldForColumn($targetColumn)] = $joinColumnValue;
                                    } else {
                                        $associatedId[$targetClass->fieldNames[$targetColumn]] = $joinColumnValue;
                                    }
                                }
                            }
                            if ( ! $associatedId) {
                                // Foreign key is NULL
                                $class->reflFields[$field]->setValue($entity, null);
                                $this->originalEntityData[$oid][$field] = null;
                            } else {
                                if (!isset($hints['fetchMode'][$class->name][$field])) {
                                    $hints['fetchMode'][$class->name][$field] = $assoc['fetch'];
                                }

                                // Foreign key is set
                                // Check identity map first
                                // FIXME: Can break easily with composite keys if join column values are in
                                //        wrong order. The correct order is the one in ClassMetadata#identifier.
                                $relatedIdHash = implode(' ', $associatedId);
                                if (isset($this->identityMap[$targetClass->rootEntityName][$relatedIdHash])) {
                                    $newValue = $this->identityMap[$targetClass->rootEntityName][$relatedIdHash];
                                    
                                    // if this is an uninitialized proxy, we are deferring eager loads,
                                    // this association is marked as eager fetch, and its an uninitialized proxy (wtf!)
                                    // then we cann append this entity for eager loading!
                                    if ($hints['fetchMode'][$class->name][$field] == ClassMetadata::FETCH_EAGER &&
                                        isset($hints['deferEagerLoad']) &&
                                        !$targetClass->isIdentifierComposite &&
                                        $newValue instanceof Proxy &&
                                        $newValue->__isInitialized__ === false) {
                                        
                                        $this->eagerLoadingEntities[$targetClass->rootEntityName][$relatedIdHash] = current($associatedId);
                                    }
                                } else {
                                    if ($targetClass->subClasses) {
                                        // If it might be a subtype, it can not be lazy. There isn't even
                                        // a way to solve this with deferred eager loading, which means putting
                                        // an entity with subclasses at a *-to-one location is really bad! (performance-wise)
                                        $newValue = $this->getEntityPersister($assoc['targetEntity'])
                                                ->loadOneToOneEntity($assoc, $entity, $associatedId);
                                    } else {
                                        // Deferred eager load only works for single identifier classes

                                        if ($hints['fetchMode'][$class->name][$field] == ClassMetadata::FETCH_EAGER) {
                                            if (isset($hints['deferEagerLoad']) && !$targetClass->isIdentifierComposite) {
                                                // TODO: Is there a faster approach?
                                                $this->eagerLoadingEntities[$targetClass->rootEntityName][$relatedIdHash] = current($associatedId);

                                                $newValue = $this->em->getProxyFactory()->getProxy($assoc['targetEntity'], $associatedId);
                                            } else {
                                                // TODO: This is very imperformant, ignore it?
                                                $newValue = $this->em->find($assoc['targetEntity'], $associatedId);
                                            }
                                        } else {
                                            $newValue = $this->em->getProxyFactory()->getProxy($assoc['targetEntity'], $associatedId);
                                        }
                                        // PERF: Inlined & optimized code from UnitOfWork#registerManaged()
                                        $newValueOid = spl_object_hash($newValue);
                                        $this->entityIdentifiers[$newValueOid] = $associatedId;
                                        $this->identityMap[$targetClass->rootEntityName][$relatedIdHash] = $newValue;
                                        $this->entityStates[$newValueOid] = self::STATE_MANAGED;
                                        // make sure that when an proxy is then finally loaded, $this->originalEntityData is set also!
                                    }
                                }
                                $this->originalEntityData[$oid][$field] = $newValue;
                                $class->reflFields[$field]->setValue($entity, $newValue);
                                
                                if ($assoc['inversedBy'] && $assoc['type'] & ClassMetadata::ONE_TO_ONE) {
                                    $inverseAssoc = $targetClass->associationMappings[$assoc['inversedBy']];
                                    $targetClass->reflFields[$inverseAssoc['fieldName']]->setValue($newValue, $entity);
                                }
                            }
                        } else {
                            // Inverse side of x-to-one can never be lazy
                            $class->reflFields[$field]->setValue($entity, $this->getEntityPersister($assoc['targetEntity'])
                                    ->loadOneToOneEntity($assoc, $entity));
                        }
                    } else {
                        // Inject collection
                        $pColl = new PersistentCollection($this->em, $targetClass, new ArrayCollection);
                        $pColl->setOwner($entity, $assoc);

                        $reflField = $class->reflFields[$field];
                        $reflField->setValue($entity, $pColl);

                        if ($assoc['fetch'] == ClassMetadata::FETCH_EAGER) {
                            $this->loadCollection($pColl);
                            $pColl->takeSnapshot();
                        } else {
                            $pColl->setInitialized(false);
                        }
                        $this->originalEntityData[$oid][$field] = $pColl;
                    }
                }
            }
        }
        
        //TODO: These should be invoked later, after hydration, because associations may not yet be loaded here.
        if (isset($class->lifecycleCallbacks[Events::postLoad])) {
            $class->invokeLifecycleCallbacks(Events::postLoad, $entity);
        }
        if ($this->evm->hasListeners(Events::postLoad)) {
            $this->evm->dispatchEvent(Events::postLoad, new LifecycleEventArgs($entity, $this->em));
        }

        return $entity;
    }

    /**
     * @return void
     */
    public function triggerEagerLoads()
    {
        if (!$this->eagerLoadingEntities) {
            return;
        }

        // avoid infinite recursion
        $eagerLoadingEntities = $this->eagerLoadingEntities;
        $this->eagerLoadingEntities = array();

        foreach ($eagerLoadingEntities AS $entityName => $ids) {
            $class = $this->em->getClassMetadata($entityName);
            $this->getEntityPersister($entityName)->loadAll(array_combine($class->identifier, array(array_values($ids))));
        }
    }

    /**
     * Initializes (loads) an uninitialized persistent collection of an entity.
     *
     * @param PeristentCollection $collection The collection to initialize.
     * @todo Maybe later move to EntityManager#initialize($proxyOrCollection). See DDC-733.
     */
    public function loadCollection(PersistentCollection $collection)
    {
        $assoc = $collection->getMapping();
        switch ($assoc['type']) {
            case ClassMetadata::ONE_TO_MANY:
                $this->getEntityPersister($assoc['targetEntity'])->loadOneToManyCollection(
                        $assoc, $collection->getOwner(), $collection);
                break;
            case ClassMetadata::MANY_TO_MANY:
                $this->getEntityPersister($assoc['targetEntity'])->loadManyToManyCollection(
                        $assoc, $collection->getOwner(), $collection);
                break;
        }
    }

    /**
     * Gets the identity map of the UnitOfWork.
     *
     * @return array
     */
    public function getIdentityMap()
    {
        return $this->identityMap;
    }

    /**
     * Gets the original data of an entity. The original data is the data that was
     * present at the time the entity was reconstituted from the database.
     *
     * @param object $entity
     * @return array
     */
    public function getOriginalEntityData($entity)
    {
        $oid = spl_object_hash($entity);
        if (isset($this->originalEntityData[$oid])) {
            return $this->originalEntityData[$oid];
        }
        return array();
    }
    
    /**
     * @ignore
     */
    public function setOriginalEntityData($entity, array $data)
    {
        $this->originalEntityData[spl_object_hash($entity)] = $data;
    }

    /**
     * INTERNAL:
     * Sets a property value of the original data array of an entity.
     *
     * @ignore
     * @param string $oid
     * @param string $property
     * @param mixed $value
     */
    public function setOriginalEntityProperty($oid, $property, $value)
    {
        $this->originalEntityData[$oid][$property] = $value;
    }

    /**
     * Gets the identifier of an entity.
     * The returned value is always an array of identifier values. If the entity
     * has a composite identifier then the identifier values are in the same
     * order as the identifier field names as returned by ClassMetadata#getIdentifierFieldNames().
     *
     * @param object $entity
     * @return array The identifier values.
     */
    public function getEntityIdentifier($entity)
    {        
        return $this->entityIdentifiers[spl_object_hash($entity)];
    }

    /**
     * Tries to find an entity with the given identifier in the identity map of
     * this UnitOfWork.
     *
     * @param mixed $id The entity identifier to look for.
     * @param string $rootClassName The name of the root class of the mapped entity hierarchy.
     * @return mixed Returns the entity with the specified identifier if it exists in
     *               this UnitOfWork, FALSE otherwise.
     */
    public function tryGetById($id, $rootClassName)
    {
        $idHash = implode(' ', (array) $id);
        if (isset($this->identityMap[$rootClassName][$idHash])) {
            return $this->identityMap[$rootClassName][$idHash];
        }
        return false;
    }

    /**
     * Schedules an entity for dirty-checking at commit-time.
     *
     * @param object $entity The entity to schedule for dirty-checking.
     * @todo Rename: scheduleForSynchronization
     */
    public function scheduleForDirtyCheck($entity)
    {
        $rootClassName = $this->em->getClassMetadata(get_class($entity))->rootEntityName;
        $this->scheduledForDirtyCheck[$rootClassName][spl_object_hash($entity)] = $entity;
    }

    /**
     * Checks whether the UnitOfWork has any pending insertions.
     *
     * @return boolean TRUE if this UnitOfWork has pending insertions, FALSE otherwise.
     */
    public function hasPendingInsertions()
    {
        return ! empty($this->entityInsertions);
    }

    /**
     * Calculates the size of the UnitOfWork. The size of the UnitOfWork is the
     * number of entities in the identity map.
     *
     * @return integer
     */
    public function size()
    {
        $count = 0;
        foreach ($this->identityMap as $entitySet) {
            $count += count($entitySet);
        }
        return $count;
    }

    /**
     * Gets the EntityPersister for an Entity.
     *
     * @param string $entityName  The name of the Entity.
     * @return Doctrine\ORM\Persisters\AbstractEntityPersister
     */
    public function getEntityPersister($entityName)
    {
        if ( ! isset($this->persisters[$entityName])) {
            $class = $this->em->getClassMetadata($entityName);
            if ($class->isInheritanceTypeNone()) {
                $persister = new Persisters\BasicEntityPersister($this->em, $class);
            } else if ($class->isInheritanceTypeSingleTable()) {
                $persister = new Persisters\SingleTablePersister($this->em, $class);
            } else if ($class->isInheritanceTypeJoined()) {
                $persister = new Persisters\JoinedSubclassPersister($this->em, $class);
            } else {
                $persister = new Persisters\UnionSubclassPersister($this->em, $class);
            }
            $this->persisters[$entityName] = $persister;
        }
        return $this->persisters[$entityName];
    }

    /**
     * Gets a collection persister for a collection-valued association.
     *
     * @param AssociationMapping $association
     * @return AbstractCollectionPersister
     */
    public function getCollectionPersister(array $association)
    {
        $type = $association['type'];
        if ( ! isset($this->collectionPersisters[$type])) {
            if ($type == ClassMetadata::ONE_TO_MANY) {
                $persister = new Persisters\OneToManyPersister($this->em);
            } else if ($type == ClassMetadata::MANY_TO_MANY) {
                $persister = new Persisters\ManyToManyPersister($this->em);
            }
            $this->collectionPersisters[$type] = $persister;
        }
        return $this->collectionPersisters[$type];
    }

    /**
     * INTERNAL:
     * Registers an entity as managed.
     *
     * @param object $entity The entity.
     * @param array $id The identifier values.
     * @param array $data The original entity data.
     */
    public function registerManaged($entity, array $id, array $data)
    {
        $oid = spl_object_hash($entity);
        $this->entityIdentifiers[$oid] = $id;
        $this->entityStates[$oid] = self::STATE_MANAGED;
        $this->originalEntityData[$oid] = $data;
        $this->addToIdentityMap($entity);
    }

    /**
     * INTERNAL:
     * Clears the property changeset of the entity with the given OID.
     *
     * @param string $oid The entity's OID.
     */
    public function clearEntityChangeSet($oid)
    {
        $this->entityChangeSets[$oid] = array();
    }

    /* PropertyChangedListener implementation */

    /**
     * Notifies this UnitOfWork of a property change in an entity.
     *
     * @param object $entity The entity that owns the property.
     * @param string $propertyName The name of the property that changed.
     * @param mixed $oldValue The old value of the property.
     * @param mixed $newValue The new value of the property.
     */
    public function propertyChanged($entity, $propertyName, $oldValue, $newValue)
    {
        $oid = spl_object_hash($entity);
        $class = $this->em->getClassMetadata(get_class($entity));

        $isAssocField = isset($class->associationMappings[$propertyName]);

        if ( ! $isAssocField && ! isset($class->fieldMappings[$propertyName])) {
            return; // ignore non-persistent fields
        }

        // Update changeset and mark entity for synchronization
        $this->entityChangeSets[$oid][$propertyName] = array($oldValue, $newValue);
        if ( ! isset($this->scheduledForDirtyCheck[$class->rootEntityName][$oid])) {
            $this->scheduleForDirtyCheck($entity);
        }
    }

    /**
     * Gets the currently scheduled entity insertions in this UnitOfWork.
     * 
     * @return array
     */
    public function getScheduledEntityInsertions()
    {
        return $this->entityInsertions;
    }
    
    /**
     * Gets the currently scheduled entity updates in this UnitOfWork.
     * 
     * @return array
     */
    public function getScheduledEntityUpdates()
    {
        return $this->entityUpdates;
    }
    
    /**
     * Gets the currently scheduled entity deletions in this UnitOfWork.
     * 
     * @return array
     */
    public function getScheduledEntityDeletions()
    {
        return $this->entityDeletions;
    }

    /**
     * Get the currently scheduled complete collection deletions
     *
     * @return array
     */
    public function getScheduledCollectionDeletions()
    {
        return $this->collectionDeletions;
    }

    /**
     * Gets the currently scheduled collection inserts, updates and deletes.
     *
     * @return array
     */
    public function getScheduledCollectionUpdates()
    {
        return $this->collectionUpdates;
    }
    
    /**
     * Helper method to initialize a lazy loading proxy or persistent collection.
     * 
     * @param object
     * @return void
     */
    public function initializeObject($obj)
    {
        if ($obj instanceof Proxy) {
            $obj->__load();
        } else if ($obj instanceof PersistentCollection) {
            $obj->initialize();
        }
    }
    
    /**
     * Helper method to show an object as string.
     * 
     * @param  object $obj
     * @return string 
     */
    private static function objToStr($obj)
    {
        return method_exists($obj, '__toString') ? (string)$obj : get_class($obj).'@'.spl_object_hash($obj);
    }
}