10. Events

Doctrine 2 features a lightweight event system that is part of the Common package.

10.1. The Event System

The event system is controlled by the EventManager. It is the central point of Doctrine’s event listener system. Listeners are registered on the manager and events are dispatched through the manager.

<?php
$evm = new EventManager();

Now we can add some event listeners to the $evm. Let’s create a EventTest class to play around with.

<?php
class EventTest
{
    const preFoo = 'preFoo';
    const postFoo = 'postFoo';

    private $_evm;

    public $preFooInvoked = false;
    public $postFooInvoked = false;

    public function __construct($evm)
    {
        $evm->addEventListener(array(self::preFoo, self::postFoo), $this);
    }

    public function preFoo(EventArgs $e)
    {
        $this->preFooInvoked = true;
    }

    public function postFoo(EventArgs $e)
    {
        $this->postFooInvoked = true;
    }
}

// Create a new instance
$test = new EventTest($evm);

Events can be dispatched by using the dispatchEvent() method.

<?php
$evm->dispatchEvent(EventTest::preFoo);
$evm->dispatchEvent(EventTest::postFoo);

You can easily remove a listener with the removeEventListener() method.

<?php
$evm->removeEventListener(array(self::preFoo, self::postFoo), $this);

The Doctrine 2 event system also has a simple concept of event subscribers. We can define a simple TestEventSubscriber class which implements the \Doctrine\Common\EventSubscriber interface and implements a getSubscribedEvents() method which returns an array of events it should be subscribed to.

<?php
class TestEventSubscriber implements \Doctrine\Common\EventSubscriber
{
    public $preFooInvoked = false;

    public function preFoo()
    {
        $this->preFooInvoked = true;
    }

    public function getSubscribedEvents()
    {
        return array(TestEvent::preFoo);
    }
}

$eventSubscriber = new TestEventSubscriber();
$evm->addEventSubscriber($eventSubscriber);

Now when you dispatch an event any event subscribers will be notified for that event.

<?php
$evm->dispatchEvent(TestEvent::preFoo);

Now you can test the $eventSubscriber instance to see if the preFoo() method was invoked.

<?php
if ($eventSubscriber->preFooInvoked) {
    echo 'pre foo invoked!';
}

10.1.1. Naming convention

Events being used with the Doctrine 2 EventManager are best named with camelcase and the value of the corresponding constant should be the name of the constant itself, even with spelling. This has several reasons:

  • It is easy to read.
  • Simplicity.
  • Each method within an EventSubscriber is named after the corresponding constant. If constant name and constant value differ, you MUST use the new value and thus, your code might be subject to codechanges when the value changes. This contradicts the intention of a constant.

An example for a correct notation can be found in the example EventTest above.

10.2. Lifecycle Events

The EntityManager and UnitOfWork trigger a bunch of events during the life-time of their registered entities.

  • preRemove - The preRemove event occurs for a given entity before the respective EntityManager remove operation for that entity is executed. It is not called for a DQL DELETE statement.
  • postRemove - The postRemove event occurs for an entity after the entity has been deleted. It will be invoked after the database delete operations. It is not called for a DQL DELETE statement.
  • prePersist - The prePersist event occurs for a given entity before the respective EntityManager persist operation for that entity is executed.
  • postPersist - The postPersist event occurs for an entity after the entity has been made persistent. It will be invoked after the database insert operations. Generated primary key values are available in the postPersist event.
  • preUpdate - The preUpdate event occurs before the database update operations to entity data. It is not called for a DQL UPDATE statement.
  • postUpdate - The postUpdate event occurs after the database update operations to entity data. It is not called for a DQL UPDATE statement.
  • postLoad - The postLoad event occurs for an entity after the entity has been loaded into the current EntityManager from the database or after the refresh operation has been applied to it.
  • loadClassMetadata - The loadClassMetadata event occurs after the mapping metadata for a class has been loaded from a mapping source (annotations/xml/yaml).
  • onFlush - The onFlush event occurs after the change-sets of all managed entities are computed. This event is not a lifecycle callback.

Warning

Note that the postLoad event occurs for an entity before any associations have been initialized. Therefore it is not safe to access associations in a postLoad callback or event handler.

You can access the Event constants from the Events class in the ORM package.

<?php
use Doctrine\ORM\Events;
echo Events::preUpdate;

These can be hooked into by two different types of event listeners:

  • Lifecycle Callbacks are methods on the entity classes that are called when the event is triggered. They receive absolutely no arguments and are specifically designed to allow changes inside the entity classes state.
  • Lifecycle Event Listeners are classes with specific callback methods that receives some kind of EventArgs instance which give access to the entity, EntityManager or other relevant data.

Note

All Lifecycle events that happen during the flush() of an EntityManager have very specific constraints on the allowed operations that can be executed. Please read the Implementing Event Listeners section very carefully to understand which operations are allowed in which lifecycle event.

10.3. Lifecycle Callbacks

A lifecycle event is a regular event with the additional feature of providing a mechanism to register direct callbacks inside the corresponding entity classes that are executed when the lifecycle event occurs.

<?php

/** @Entity @HasLifecycleCallbacks */
class User
{
    // ...

    /**
     * @Column(type="string", length=255)
     */
    public $value;

    /** @Column(name="created_at", type="string", length=255) */
    private $createdAt;

    /** @PrePersist */
    public function doStuffOnPrePersist()
    {
        $this->createdAt = date('Y-m-d H:m:s');
    }

    /** @PrePersist */
    public function doOtherStuffOnPrePersist()
    {
        $this->value = 'changed from prePersist callback!';
    }

    /** @PostPersist */
    public function doStuffOnPostPersist()
    {
        $this->value = 'changed from postPersist callback!';
    }

    /** @PostLoad */
    public function doStuffOnPostLoad()
    {
        $this->value = 'changed from postLoad callback!';
    }

    /** @PreUpdate */
    public function doStuffOnPreUpdate()
    {
        $this->value = 'changed from preUpdate callback!';
    }
}

Note that when using annotations you have to apply the @HasLifecycleCallbacks marker annotation on the entity class.

If you want to register lifecycle callbacks from YAML or XML you can do it with the following.

User:
  type: entity
  fields:
# ...
    name:
      type: string(50)
  lifecycleCallbacks:
    prePersist: [ doStuffOnPrePersist, doOtherStuffOnPrePersistToo ]
    postPersist: [ doStuffOnPostPersist ]

XML would look something like this:

<?xml version="1.0" encoding="UTF-8"?>

<doctrine-mapping xmlns="http://doctrine-project.org/schemas/orm/doctrine-mapping"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://doctrine-project.org/schemas/orm/doctrine-mapping
                          /Users/robo/dev/php/Doctrine/doctrine-mapping.xsd">

    <entity name="User">

        <lifecycle-callbacks>
            <lifecycle-callback type="prePersist" method="doStuffOnPrePersist"/>
            <lifecycle-callback type="postPersist" method="doStuffOnPostPersist"/>
        </lifecycle-callbacks>

    </entity>

</doctrine-mapping>

You just need to make sure a public doStuffOnPrePersist() and doStuffOnPostPersist() method is defined on your User model.

<?php
// ...

class User
{
    // ...

    public function doStuffOnPrePersist()
    {
        // ...
    }

    public function doStuffOnPostPersist()
    {
        // ...
    }
}

The key of the lifecycleCallbacks is the name of the method and the value is the event type. The allowed event types are the ones listed in the previous Lifecycle Events section.

10.4. Listening to Lifecycle Events

Lifecycle event listeners are much more powerful than the simple lifecycle callbacks that are defined on the entity classes. They allow to implement re-usable behaviors between different entity classes, yet require much more detailed knowledge about the inner workings of the EntityManager and UnitOfWork. Please read the Implementing Event Listeners section carefully if you are trying to write your own listener.

To register an event listener you have to hook it into the EventManager that is passed to the EntityManager factory:

<?php
$eventManager = new EventManager();
$eventManager->addEventListener(array(Events::preUpdate), MyEventListener());
$eventManager->addEventSubscriber(new MyEventSubscriber());

$entityManager = EntityManager::create($dbOpts, $config, $eventManager);

You can also retrieve the event manager instance after the EntityManager was created:

<?php
$entityManager->getEventManager()->addEventListener(array(Events::preUpdate), MyEventListener());
$entityManager->getEventManager()->addEventSubscriber(new MyEventSubscriber());

10.5. Implementing Event Listeners

This section explains what is and what is not allowed during specific lifecycle events of the UnitOfWork. Although you get passed the EntityManager in all of these events, you have to follow this restrictions very carefully since operations in the wrong event may produce lots of different errors, such as inconsistent data and lost updates/persists/removes.

For the described events that are also lifecycle callback events the restrictions apply as well, with the additional restriction that you do not have access to the EntityManager or UnitOfWork APIs inside these events.

10.5.1. prePersist

There are two ways for the prePersist event to be triggered. One is obviously when you call EntityManager#persist(). The event is also called for all cascaded associations.

There is another way for prePersist to be called, inside the flush() method when changes to associations are computed and this association is marked as cascade persist. Any new entity found during this operation is also persisted and prePersist called on it. This is called “persistence by reachability”.

In both cases you get passed a LifecycleEventArgs instance which has access to the entity and the entity manager.

The following restrictions apply to prePersist:

  • If you are using a PrePersist Identity Generator such as sequences the ID value will NOT be available within any PrePersist events.
  • Doctrine will not recognize changes made to relations in a pre persist event called by “reachability” through a cascade persist unless you use the internal UnitOfWork API. We do not recommend such operations in the persistence by reachability context, so do this at your own risk and possibly supported by unit-tests.

10.5.2. preRemove

The preRemove event is called on every entity when its passed to the EntityManager#remove() method. It is cascaded for all associations that are marked as cascade delete.

There are no restrictions to what methods can be called inside the preRemove event, except when the remove method itself was called during a flush operation.

10.5.3. onFlush

OnFlush is a very powerful event. It is called inside EntityManager#flush() after the changes to all the managed entities and their associations have been computed. This means, the onFlush event has access to the sets of:

  • Entities scheduled for insert
  • Entities scheduled for update
  • Entities scheduled for removal
  • Collections scheduled for update
  • Collections scheduled for removal

To make use of the onFlush event you have to be familiar with the internal UnitOfWork API, which grants you access to the previously mentioned sets. See this example:

<?php
class FlushExampleListener
{
    public function onFlush(OnFlushEventArgs $eventArgs)
    {
        $em = $eventArgs->getEntityManager();
        $uow = $em->getUnitOfWork();

        foreach ($uow->getScheduledEntityInsertions() AS $entity) {

        }

        foreach ($uow->getScheduledEntityUpdates() AS $entity) {

        }

        foreach ($uow->getScheduledEntityDeletions() AS $entity) {

        }

        foreach ($uow->getScheduledCollectionDeletions() AS $col) {

        }

        foreach ($uow->getScheduledCollectionUpdates() AS $col) {

        }
    }
}

The following restrictions apply to the onFlush event:

  • Calling EntityManager#persist() does not suffice to trigger a persist on an entity. You have to execute an additional call to $unitOfWork->computeChangeSet($classMetadata, $entity).
  • Changing primitive fields or associations requires you to explicitly trigger a re-computation of the changeset of the affected entity. This can be done by either calling $unitOfWork->computeChangeSet($classMetadata, $entity) or $unitOfWork->recomputeSingleEntityChangeSet($classMetadata, $entity). The second method has lower overhead, but only re-computes primitive fields, never associations.

10.5.4. preUpdate

PreUpdate is the most restrictive to use event, since it is called right before an update statement is called for an entity inside the EntityManager#flush() method.

Changes to associations of the updated entity are never allowed in this event, since Doctrine cannot guarantee to correctly handle referential integrity at this point of the flush operation. This event has a powerful feature however, it is executed with a PreUpdateEventArgs instance, which contains a reference to the computed change-set of this entity.

This means you have access to all the fields that have changed for this entity with their old and new value. The following methods are available on the PreUpdateEventArgs:

  • getEntity() to get access to the actual entity.
  • getEntityChangeSet() to get a copy of the changeset array. Changes to this returned array do not affect updating.
  • hasChangedField($fieldName) to check if the given field name of the current entity changed.
  • getOldValue($fieldName) and getNewValue($fieldName) to access the values of a field.
  • setNewValue($fieldName, $value) to change the value of a field to be updated.

A simple example for this event looks like:

<?php
class NeverAliceOnlyBobListener
{
    public function preUpdate(PreUpdateEventArgs $eventArgs)
    {
        if ($eventArgs->getEntity() instanceof User) {
            if ($eventArgs->hasChangedField('name') && $eventArgs->getNewValue('name') == 'Alice') {
                $eventArgs->setNewValue('name', 'Bob');
            }
        }
    }
}

You could also use this listener to implement validation of all the fields that have changed. This is more efficient than using a lifecycle callback when there are expensive validations to call:

<?php
class ValidCreditCardListener
{
    public function preUpdate(PreUpdateEventArgs $eventArgs)
    {
        if ($eventArgs->getEntity() instanceof Account) {
            if ($eventArgs->hasChangedField('creditCard')) {
                $this->validateCreditCard($eventArgs->getNewValue('creditCard'));
            }
        }
    }

    private function validateCreditCard($no)
    {
        // throw an exception to interrupt flush event. Transaction will be rolled back.
    }
}

Restrictions for this event:

  • Changes to associations of the passed entities are not recognized by the flush operation anymore.
  • Changes to fields of the passed entities are not recognized by the flush operation anymore, use the computed change-set passed to the event to modify primitive field values.
  • Any calls to EntityManager#persist() or EntityManager#remove(), even in combination with the UnitOfWork API are strongly discouraged and don’t work as expected outside the flush operation.

10.5.5. postUpdate, postRemove, postPersist

The three post events are called inside EntityManager#flush(). Changes in here are not relevant to the persistence in the database, but you can use this events to

10.5.6. postLoad

This event is called after an entity is constructed by the EntityManager.

10.6. Load ClassMetadata Event

When the mapping information for an entity is read, it is populated in to a ClassMetadataInfo instance. You can hook in to this process and manipulate the instance.

<?php
$test = new EventTest();
$metadataFactory = $em->getMetadataFactory();
$evm = $em->getEventManager();
$evm->addEventListener(Events::loadClassMetadata, $test);

class EventTest
{
    public function loadClassMetadata(\Doctrine\ORM\Event\LoadClassMetadataEventArgs $eventArgs)
    {
        $classMetadata = $eventArgs->getClassMetadata();
        $fieldMapping = array(
            'fieldName' => 'about',
            'type' => 'string',
            'length' => 255
        );
        $classMetadata->mapField($fieldMapping);
    }
}



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