Event Listeners

Introduction

Doctrine provides flexible event listener architecture that not only allows listening for different events but also for altering the execution of the listened methods.

There are several different listeners and hooks for various Doctrine components. Listeners are separate classes whereas hooks are empty template methods within the listened class.

Hooks are simpler than event listeners but they lack the separation of different aspects. An example of using Doctrine_Record hooks:

// models/BlogPost.php

class BlogPost extends Doctrine_Record
{
    // ...

    public function preInsert($event)
    {
        $invoker = $event->getInvoker();

        $invoker->created = date('Y-m-d', time());
    }
}

Now you can use the above model with the following code assuming we added a title, body and created column to the model:

// test.php

// ...
$ blog        = new BlogPost();
$ blog->title = 'New title';
$ blog->body  = 'Some content';
$ blog->save();

echo $blog->created;

The above example will output the current date as PHP knows it.

Each listener and hook method takes one parameter Doctrine_Event object. Doctrine_Event object holds information about the event in question and can alter the execution of the listened method.

For the purposes of this documentation many method tables are provided with column named params indicating names of the parameters that an event object holds on given event. For example the preCreateSavepoint event has one parameter with the name of the created savepoint, which is quite intuitively named as savepoint.

Connection Listeners

Connection listeners are used for listening the methods of Doctrine_Connection and its modules (such as Doctrine_Transaction). All listener methods take one argument Doctrine_Event which holds information about the listened event.

class MyListener extends Doctrine_EventListener
{
    public function preExec( Doctrine_Event $event )
    {

    }
}

class MyListener implements Doctrine_EventListener_Interface
{
    public function preTransactionCommit( Doctrine_Event $event ) {}
    public function postTransactionCommit( Doctrine_Event $event ) {}

    public function preTransactionRollback( Doctrine_Event $event ) {}
    public function postTransactionRollback( Doctrine_Event $event ) {}

    public function preTransactionBegin( Doctrine_Event $event ) {}
    public function postTransactionBegin( Doctrine_Event $event ) {}

    public function postConnect( Doctrine_Event $event ) {}
    public function preConnect( Doctrine_Event $event ) {}

    public function preQuery( Doctrine_Event $event ) {}
    public function postQuery( Doctrine_Event $event ) {}

    public function prePrepare( Doctrine_Event $event ) {}
    public function postPrepare( Doctrine_Event $event ) {}

    public function preExec( Doctrine_Event $event ) {}
    public function postExec( Doctrine_Event $event ) {}

    public function preError( Doctrine_Event $event ) {}
    public function postError( Doctrine_Event $event ) {}

    public function preFetch( Doctrine_Event $event ) {}
    public function postFetch( Doctrine_Event $event ) {}

    public function preFetchAll( Doctrine_Event $event ) {}
    public function postFetchAll( Doctrine_Event $event ) {}

    public function preStmtExecute( Doctrine_Event $event ) {}
    public function postStmtExecute( Doctrine_Event $event ) {}
}

class MyDebugger implements Doctrine_Overloadable
{
    public function __call( $methodName, $args )
    {
        echo $methodName . ' called !';
    }
}

$ conn->setListener( new MyDebugger() );

$ conn->addListener( new MyDebugger() );
$ conn->addListener( new MyLogger() );

class MyTransactionListener extends Doctrine_EventListener
{
    public function preTransactionBegin( Doctrine_Event $event )
    {
        echo 'beginning transaction... ';
    }

    public function preTransactionRollback( Doctrine_Event $event )
    {
        echo 'rolling back transaction... ';
    }
}

Hydration Listeners

The hydration listeners can be used for listening to resultset hydration procedures. Two methods exist for listening to the hydration procedure: preHydrate() and postHydrate().

If you set the hydration listener on connection level the code within the preHydrate() and postHydrate() blocks will be invoked by all components within a multi-component resultset. However if you add a similar listener on table level it only gets invoked when the data of that table is being hydrated.

Consider we have a class called User with the following fields: first_name, last_name and age. In the following example we create a listener that always builds a generated field called full_name based on first_name and last_name fields.

// test.php

// ...
class HydrationListener extends Doctrine_Record_Listener
{
    public function preHydrate( Doctrine_Event $event )
    {
        $data              = $event->data;
        $data['full_name'] = $data['first_name'] . ' ' . $data['last_name'];
        $event->data       = $data;
    }
}

Now all we need to do is attach this listener to the User record and fetch some users:

// test.php

// ...
$ userTable = Doctrine_Core::getTable('User');
$ userTable->addRecordListener( new HydrationListener() );

$ q = Doctrine_Query::create()
    ->from('User');

$ users = $q->execute();

foreach ( $users as $user )
{
    echo $user->full_name;
}

Record Listeners

Doctrine_Record provides listeners very similar to Doctrine_Connection. You can set the listeners at global, connection and table level.

Here is a list of all available listener methods:

All of the below listeners are invoked in the Doctrine_Record and Doctrine_Validator classes. And they are all passed an instance of Doctrine_Event.

Just like with connection listeners there are three ways of defining a record listener: by extending Doctrine_Record_Listener, by implementing Doctrine_Record_Listener_Interface or by implementing Doctrine_Overloadable.

In the following we'll create a global level listener by implementing Doctrine_Overloadable:

class Logger implements Doctrine_Overloadable
{
    public function __call( $m, $a )
    {
        echo 'caught event ' . $m;

        // do some logging here...
    }
}

Attaching the listener to manager is easy:

$ manager->addRecordListener( new Logger() );

Note that by adding a manager level listener it affects on all connections and all tables / records within these connections. In the following we create a connection level listener:

class Debugger extends Doctrine_Record_Listener
{
    public function preInsert( Doctrine_Event $event )
    {
        echo 'inserting a record ...';
    }

    public function preUpdate( Doctrine_Event $event )
    {
        echo 'updating a record...';
    }
}

Attaching the listener to a connection is as easy as:

$ conn->addRecordListener( new Debugger() );

Many times you want the listeners to be table specific so that they only apply on the actions on that given table.

Here is an example:

class Debugger extends Doctrine_Record_Listener
{
    public function postDelete( Doctrine_Event $event )
    {
        echo 'deleted ' . $event->getInvoker()->id;
    }
}

Attaching this listener to given table can be done as follows:

class MyRecord extends Doctrine_Record
{
    // ...
    public function setUp()
    {
        $this->addListener( new Debugger() );
    }
}

Record Hooks

All of the below listeners are invoked in the Doctrine_Record and Doctrine_Validator classes. And they are all passed an instance of Doctrine_Event.

Here is a simple example where we make use of the preInsert() and preUpdate() methods:

class BlogPost extends Doctrine_Record
{
    public function setTableDefinition()
    {
        $this->hasColumn( 'title', 'string', 200 );
        $this->hasColumn( 'content', 'string' );
        $this->hasColumn( 'created', 'date' );
        $this->hasColumn( 'updated', 'date' );
    }

    public function preInsert( $event )
    {
        $this->created = date( 'Y-m-d', time() );
    }

    public function preUpdate( $event )
    {
        $this->updated = date( 'Y-m-d', time() );
    }
}

DQL Hooks

Doctrine allows you to attach record listeners globally, on each connection, or on specific record instances. Doctrine_Query implements preDql*() hooks which are checked for on any attached record listeners and checked for on the model instance itself whenever a query is executed. The query will check all models involved in the from part of the query for any hooks which can alter the query that invoked the hook.

Here is a list of the hooks you can use with DQL:

Below is an example record listener attached directly to the model which will implement the SoftDelete functionality for the User model.

class UserListener extends Doctrine_EventListener
{
    /**
     * Skip the normal delete options so we can override it with our own
     *
     * @param Doctrine_Event $event
     * @return void
     */
    public function preDelete( Doctrine_Event $event )
    {
        $event->skipOperation();
    }

    /**
     * Implement postDelete() hook and set the deleted flag to true
     *
     * @param Doctrine_Event $event
     * @return void
     */
    public function postDelete( Doctrine_Event $event )
    {
        $name                       = $this->_options['name'];
        $event->getInvoker()->$name = true;
        $event->getInvoker()->save();
    }

    /**
     * Implement preDqlDelete() hook and modify a dql delete query so it updates the deleted flag
     * instead of deleting the record
     *
     * @param Doctrine_Event $event
     * @return void
     */
    public function preDqlDelete( Doctrine_Event $event )
    {
        $params = $event->getParams();
        $field  = $params['alias'] . '.deleted';
        $q      = $event->getQuery();

        if ( ! $q->contains( $field ) )
        {
            $q->from('')->update( $params['component'] . ' ' . $params['alias'] );
            $q->set( $field, '?', array(false) );
            $q->addWhere( $field . ' = ?', array(true) );
        }
    }

    /**
     * Implement preDqlDelete() hook and add the deleted flag to all queries for which this model
     * is being used in.
     *
     * @param Doctrine_Event $event
     * @return void
     */
    public function preDqlSelect( Doctrine_Event $event )
    {
        $params = $event->getParams();
        $field  = $params['alias'] . '.deleted';
        $q      = $event->getQuery();

        if ( ! $q->contains( $field ) )
        {
            $q->addWhere( $field . ' = ?', array(false) );
        }
    }
}

All of the above methods in the listener could optionally be placed in the user class below. Doctrine will check there for the hooks as well:

class User extends Doctrine_Record
{
    // ...
    public function preDqlSelect()
    {
        // ...
    }

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

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

In order for these dql callbacks to be checked, you must explicitly turn them on. Because this adds a small amount of overhead for each query, we have it off by default. We already enabled this attribute in an earlier chapter.

Here it is again to refresh your memory:

// bootstrap.php

// ...
$ manager->setAttribute( Doctrine_Core::ATTR_USE_DQL_CALLBACKS, true );

Now when you interact with the User model it will take in to account the deleted flag:

Delete user through record instance:

$ user           = new User();
$ user->username = 'jwage';
$ user->password = 'changeme';
$ user->save();
$ user->delete();

$ q = Doctrine_Query::create()
    ->from('User u');

echo $q->getSqlQuery();

SELECT
u.id AS u**id,
u.username AS u**username,
u.password AS u**password,
u.deleted AS u**deleted
FROM user u
WHERE u.deleted = ?

Chaining Listeners

Doctrine allows chaining of different event listeners. This means that more than one listener can be attached for listening the same events. The following example attaches two listeners for given connection:

In this example Debugger and Logger both inherit Doctrine_EventListener:

$ conn->addListener( new Debugger() );
$ conn->addListener( new Logger() );

The Event object

class MyListener extends Doctrine_EventListener
{
    public function preExec( Doctrine_Event $event )
    {
        $event->getInvoker(); // Doctrine_Connection
    }
}

class MyListener extends Doctrine_EventListener
{
    public function preExec( Doctrine_Event $event )
    {
        $event->getCode(); // Doctrine_Event::CONN_EXEC
    }
}

class MyRecord extends Doctrine_Record
{
    public function preUpdate( Doctrine_Event $event )
    {
        $event->getCode(); // Doctrine_Event::RECORD_UPDATE
    }
}

class MyRecord extends Doctrine_Record
{
    public function preUpdate( Doctrine_Event $event )
    {
        $event->getInvoker(); // Object(MyRecord)
    }
}

class MyListener extends Doctrine_EventListener
{
    public function preExec( Doctrine_Event $event )
    {
        // some business logic, then:
        $event->skipOperation();
    }
}

class MyListener extends Doctrine_EventListener
{
    public function preExec( Doctrine_Event $event )
    {
        // some business logic, then:
        $event->skipNextListener();
    }
}

Conclusion

Event listeners are a great feature in Doctrine and combined with Behaviors they can provide some very complex functionality with a minimal amount of code.

Now we are ready to move on to discuss the best feature in Doctrine for improving performance, Caching.