Doctrine Events

Name: SymfonyCon Vienna 2024
Start: 2024-12-05
End: 2024-12-06

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Doctrine Events

Doctrine, the set of PHP libraries used by Symfony to work with databases, provides a lightweight event system to update entities during the application execution. These events, called lifecycle events, allow to perform tasks such as "update the createdAt property automatically right before persisting entities of this type".

Doctrine triggers events before/after performing the most common entity operations (e.g. prePersist/postPersist, preUpdate/postUpdate) and also on other common tasks (e.g. loadClassMetadata, onClear).

There are different ways to listen to these Doctrine events:

Lifecycle callbacks, they are defined as public methods on the entity classes and they are called when the events are triggered;
Lifecycle listeners and subscribers, they are classes with callback methods for one or more events and they are called for all entities;
Entity listeners, they are similar to lifecycle listeners, but they are called only for the entities of a certain class.

These are the drawbacks and advantages of each one:

Callbacks have better performance because they only apply to a single entity class, but you can't reuse the logic for different entities and they don't have access to Symfony services;
Lifecycle listeners and subscribers can reuse logic among different entities and can access Symfony services but their performance is worse because they are called for all entities;
Entity listeners have the same advantages of lifecycle listeners and they have better performance because they only apply to a single entity class.

This article only explains the basics about Doctrine events when using them inside a Symfony application. Read the official docs about Doctrine events to learn everything about them.

Doctrine Lifecycle Callbacks

Lifecycle callbacks are defined as public methods inside the entity you want to modify. For example, suppose you want to set a createdAt date column to the current date, but only when the entity is first persisted (i.e. inserted). To do so, define a callback for the prePersist Doctrine event:

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        // src/Entity/Product.php
namespace App\Entity;

use Doctrine\ORM\Mapping as ORM;

// When using attributes, don't forget to add #[ORM\HasLifecycleCallbacks]
// to the class of the entity where you define the callback

#[ORM\Entity]
#[ORM\HasLifecycleCallbacks]
class Product
{
    // ...

    #[ORM\PrePersist]
    public function setCreatedAtValue(): void
    {
        $this->createdAt = new \DateTimeImmutable();
    }
}
    

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        # config/doctrine/Product.orm.yml
App\Entity\Product:
    type: entity
    # ...
    lifecycleCallbacks:
        prePersist: ['setCreatedAtValue']
    

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        <!-- config/doctrine/Product.orm.xml -->
<?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
        https://doctrine-project.org/schemas/orm/doctrine-mapping.xsd">

    <entity name="App\Entity\Product">
        <!-- ... -->
        <lifecycle-callbacks>
            <lifecycle-callback type="prePersist" method="setCreatedAtValue"/>
        </lifecycle-callbacks>
    </entity>
</doctrine-mapping>
    

Note

Some lifecycle callbacks receive an argument that provides access to useful information such as the current entity manager (e.g. the preUpdate callback receives a PreUpdateEventArgs $event argument).

Doctrine Lifecycle Listeners

Lifecycle listeners are defined as PHP classes that listen to a single Doctrine event on all the application entities. For example, suppose that you want to update some search index whenever a new entity is persisted in the database. To do so, define a listener for the postPersist Doctrine event:

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        // src/EventListener/SearchIndexer.php
namespace App\EventListener;

use App\Entity\Product;
use Doctrine\Persistence\Event\LifecycleEventArgs;

class SearchIndexer
{
    // the listener methods receive an argument which gives you access to
    // both the entity object of the event and the entity manager itself
    public function postPersist(LifecycleEventArgs $args): void
    {
        $entity = $args->getObject();

        // if this listener only applies to certain entity types,
        // add some code to check the entity type as early as possible
        if (!$entity instanceof Product) {
            return;
        }

        $entityManager = $args->getObjectManager();
        // ... do something with the Product entity
    }
}
    

The next step is to enable the Doctrine listener in the Symfony application by creating a new service for it and tagging it with the doctrine.event_listener tag:

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        # config/services.yaml
services:
    # ...

    App\EventListener\SearchIndexer:
        tags:
            -
                name: 'doctrine.event_listener'
                # this is the only required option for the lifecycle listener tag
                event: 'postPersist'

                # listeners can define their priority in case multiple subscribers or listeners are associated
                # to the same event (default priority = 0; higher numbers = listener is run earlier)
                priority: 500

                # you can also restrict listeners to a specific Doctrine connection
                connection: 'default'
    

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        <!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:doctrine="http://symfony.com/schema/dic/doctrine">
    <services>
        <!-- ... -->

        <!--
            * 'event' is the only required option that defines the lifecycle listener
            * 'priority': used when multiple subscribers or listeners are associated to the same event
            *             (default priority = 0; higher numbers = listener is run earlier)
            * 'connection': restricts the listener to a specific Doctrine connection
        -->
        <service id="App\EventListener\SearchIndexer">
            <tag name="doctrine.event_listener"
                event="postPersist"
                priority="500"
                connection="default"/>
        </service>
    </services>
</container>
    

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        // config/services.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

use App\EventListener\SearchIndexer;

return static function (ContainerConfigurator $containerConfigurator) {
    $services = $containerConfigurator->services();

    // listeners are applied by default to all Doctrine connections
    $services->set(SearchIndexer::class)
        ->tag('doctrine.event_listener', [
            // this is the only required option for the lifecycle listener tag
            'event' => 'postPersist',

            // listeners can define their priority in case multiple subscribers or listeners are associated
            // to the same event (default priority = 0; higher numbers = listener is run earlier)
            'priority' => 500,

            # you can also restrict listeners to a specific Doctrine connection
            'connection' => 'default',
        ])
    ;
};
    

Tip

Symfony loads (and instantiates) Doctrine listeners only when the related Doctrine event is actually fired; whereas Doctrine subscribers are always loaded (and instantiated) by Symfony, making them less performant.

Tip

The value of the connection option can also be a configuration parameter.

Doctrine Entity Listeners

Entity listeners are defined as PHP classes that listen to a single Doctrine event on a single entity class. For example, suppose that you want to send some notifications whenever a User entity is modified in the database.

First, define a PHP class that handles the postUpdate Doctrine event:

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        // src/EventListener/UserChangedNotifier.php
namespace App\EventListener;

use App\Entity\User;
use Doctrine\Persistence\Event\LifecycleEventArgs;

class UserChangedNotifier
{
    // the entity listener methods receive two arguments:
    // the entity instance and the lifecycle event
    public function postUpdate(User $user, LifecycleEventArgs $event): void
    {
        // ... do something to notify the changes
    }
}
    

Then, add the #[AsEntityListener] attribute to the class to enable it as a Doctrine entity listener in your application:

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        // src/EventListener/UserChangedNotifier.php
namespace App\EventListener;

// ...
use App\Entity\User;
use Doctrine\Bundle\DoctrineBundle\Attribute\AsEntityListener;
use Doctrine\ORM\Events;

#[AsEntityListener(event: Events::postUpdate, method: 'postUpdate', entity: User::class)]
class UserChangedNotifier
{
    // ...
}
    

That's it. Alternatively, if you prefer to not use PHP attributes, you must configure a service for the entity listener and tag it with the doctrine.orm.entity_listener tag as follows:

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        # config/services.yaml
services:
    # ...

    App\EventListener\UserChangedNotifier:
        tags:
            -
                # these are the options required to define the entity listener
                name: 'doctrine.orm.entity_listener'
                event: 'postUpdate'
                entity: 'App\Entity\User'

                # these are other options that you may define if needed

                # set the 'lazy' option to TRUE to only instantiate listeners when they are used
                # lazy: true

                # set the 'entity_manager' option if the listener is not associated to the default manager
                # entity_manager: 'custom'

                # by default, Symfony looks for a method called after the event (e.g. postUpdate())
                # if it doesn't exist, it tries to execute the '__invoke()' method, but you can
                # configure a custom method name with the 'method' option
                # method: 'checkUserChanges'
    

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        <!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:doctrine="http://symfony.com/schema/dic/doctrine">
    <services>
        <!-- ... -->

        <service id="App\EventListener\UserChangedNotifier">
            <!--
                * These are the options required to define the entity listener:
                *   * name
                *   * event
                *   * entity
                *
                * These are other options that you may define if needed:
                *   * lazy: if TRUE, listeners are only instantiated when they are used
                *   * entity_manager: define it if the listener is not associated to the default manager
                *   * method: by default, Symfony looks for a method called after the event (e.g. postUpdate())
                *           if it doesn't exist, it tries to execute the '__invoke()' method, but
                *           you can configure a custom method name with the 'method' option
            -->
            <tag name="doctrine.orm.entity_listener"
                event="postUpdate"
                entity="App\Entity\User"
                lazy="true"
                entity_manager="custom"
                method="checkUserChanges"/>
        </service>
    </services>
</container>
    

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        // config/services.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

use App\Entity\User;
use App\EventListener\UserChangedNotifier;

return static function (ContainerConfigurator $containerConfigurator) {
    $services = $containerConfigurator->services();

    $services->set(UserChangedNotifier::class)
        ->tag('doctrine.orm.entity_listener', [
            // These are the options required to define the entity listener:
            'event' => 'postUpdate',
            'entity' => User::class,

            // These are other options that you may define if needed:

            // set the 'lazy' option to TRUE to only instantiate listeners when they are used
            // 'lazy' => true,

            // set the 'entity_manager' option if the listener is not associated to the default manager
            // 'entity_manager' => 'custom',

            // by default, Symfony looks for a method called after the event (e.g. postUpdate())
            // if it doesn't exist, it tries to execute the '__invoke()' method, but you can
            // configure a custom method name with the 'method' option
            // 'method' => 'checkUserChanges',
        ])
    ;
};
    

Doctrine Lifecycle Subscribers

Lifecycle subscribers are defined as PHP classes that implement the Doctrine\Common\EventSubscriber interface and which listen to one or more Doctrine events on all the application entities. For example, suppose that you want to log all the database activity. To do so, define a subscriber for the postPersist, postRemove and postUpdate Doctrine events:

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        // src/EventListener/DatabaseActivitySubscriber.php
namespace App\EventListener;

use App\Entity\Product;
use Doctrine\Bundle\DoctrineBundle\EventSubscriber\EventSubscriberInterface;
use Doctrine\ORM\Events;
use Doctrine\Persistence\Event\LifecycleEventArgs;

class DatabaseActivitySubscriber implements EventSubscriberInterface
{
    // this method can only return the event names; you cannot define a
    // custom method name to execute when each event triggers
    public function getSubscribedEvents(): array
    {
        return [
            Events::postPersist,
            Events::postRemove,
            Events::postUpdate,
        ];
    }

    // callback methods must be called exactly like the events they listen to;
    // they receive an argument of type LifecycleEventArgs, which gives you access
    // to both the entity object of the event and the entity manager itself
    public function postPersist(LifecycleEventArgs $args): void
    {
        $this->logActivity('persist', $args);
    }

    public function postRemove(LifecycleEventArgs $args): void
    {
        $this->logActivity('remove', $args);
    }

    public function postUpdate(LifecycleEventArgs $args): void
    {
        $this->logActivity('update', $args);
    }

    private function logActivity(string $action, LifecycleEventArgs $args): void
    {
        $entity = $args->getObject();

        // if this subscriber only applies to certain entity types,
        // add some code to check the entity type as early as possible
        if (!$entity instanceof Product) {
            return;
        }

        // ... get the entity information and log it somehow
    }
}
    

If you're using the default services.yaml configuration and DoctrineBundle 2.1 (released May 25, 2020) or newer, this example will already work! Otherwise, create a service for this subscriber and tag it with doctrine.event_subscriber.

If you need to configure some option of the subscriber (e.g. its priority or Doctrine connection to use) you must do that in the manual service configuration:

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        # config/services.yaml
services:
    # ...

    App\EventListener\DatabaseActivitySubscriber:
        tags:
            - name: 'doctrine.event_subscriber'

              # subscribers can define their priority in case multiple subscribers or listeners are associated
              # to the same event (default priority = 0; higher numbers = listener is run earlier)
              priority: 500

              # you can also restrict listeners to a specific Doctrine connection
              connection: 'default'
    

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        <!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:doctrine="http://symfony.com/schema/dic/doctrine">
    <services>
        <!-- ... -->

        <!--
            * 'priority': used when multiple subscribers or listeners are associated to the same event
            *             (default priority = 0; higher numbers = listener is run earlier)
            * 'connection': restricts the listener to a specific Doctrine connection
        -->
        <service id="App\EventListener\DatabaseActivitySubscriber">
            <tag name="doctrine.event_subscriber" priority="500" connection="default"/>
        </service>
    </services>
</container>
    

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        // config/services.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

use App\EventListener\DatabaseActivitySubscriber;

return static function (ContainerConfigurator $containerConfigurator) {
    $services = $containerConfigurator->services();

    $services->set(DatabaseActivitySubscriber::class)
        ->tag('doctrine.event_subscriber'[
            // subscribers can define their priority in case multiple subscribers or listeners are associated
            // to the same event (default priority = 0; higher numbers = listener is run earlier)
            'priority' => 500,

            // you can also restrict listeners to a specific Doctrine connection
            'connection' => 'default',
        ])
    ;
};
    

Tip

Symfony loads (and instantiates) Doctrine subscribers whenever the application executes; whereas Doctrine listeners are only loaded when the related event is actually fired, making them more performant.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.

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