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By Jonathan H. Wage

Writing a Doctrine Behavior

In this section we will demonstrate how you can write a behavior using Doctrine 1.2. We'll create an example that allows you to easily maintain a cached count of relationships so that you don't have to query the count every single time.

The functionality is quite simple. For all the relationships you want to maintain a count for, the behavior will add a column to the model to store the current count.

The Schema

Here is the schema we will use to start with. Later we will modify this and add the actAs definition for the behavior we are about to write:

# config/doctrine/schema.yml
Thread:
  columns:
    title:
      type: string(255)
      notnull: true
 
Post:
  columns:
    thread_id:
      type: integer
      notnull: true
    body:
      type: clob
      notnull: true
  relations:
    Thread:
      onDelete: CASCADE
      foreignAlias: Posts

Now we can build everything for that schema:

$ php symfony doctrine:build --all

The Template

First we need to write the basic Doctrine_Template child class that will be responsible for adding the columns to the model that will store the counts.

You can simply put this somewhere in one of the project lib/ directories and symfony will be able to autoload it for you:

// lib/count_cache/CountCache.class.php
class CountCache extends Doctrine_Template
{
  public function setTableDefinition()
  {
  }
 
  public function setUp()
  {
  }
}

Now let's modify the Post model to actAs the CountCache behavior:

# config/doctrine/schema.yml
Post:
  actAs:
    CountCache: ~
  # ...

Now that we have the Post model using the CountCache behavior let me explain a little about what happens with it.

When the mapping information for a model is instantiated, any attached behaviors get the setTableDefinition() and setUp() methods invoked. Just like you have in the BasePost class in lib/model/doctrine/base/BasePost.class.php. This allows you to add things to any model in a plug n' play fashion. This can be columns, relationships, event listeners, etc.

Now that you understand a little bit about what is happening, let's make the CountCache behavior actually do something:

class CountCache extends Doctrine_Template
{
  protected $_options = array(
    'relations' => array()
  );
 
  public function setTableDefinition()
  {
    foreach ($this->_options['relations'] as $relation => $options)
    {
      // Build column name if one is not given
      if (!isset($options['columnName']))
      {
        $this->_options['relations'][$relation]['columnName'] = 'num_'.Doctrine_Inflector::tableize($relation);
      }
 
      // Add the column to the related model
      $columnName = $this->_options['relations'][$relation]['columnName'];
      $relatedTable = $this->_table->getRelation($relation)->getTable();
      $this->_options['relations'][$relation]['className'] = $relatedTable->getOption('name');
      $relatedTable->setColumn($columnName, 'integer', null, array('default' => 0));
    }
  }
}

The above code will now add columns to maintain the count on the related model. So in our case, we're adding the behavior to the Post model for the Thread relationship. We want to maintain the number of posts any given Thread instance has in a column named num_posts. So now modify the YAML schema to define the extra options for the behavior:

# ...
 
Post:
  actAs:
    CountCache:
      relations:
        Thread:
          columnName: num_posts
          foreignAlias: Posts
  # ...

Now the Thread model has a num_posts column that we will keep up to date with the number of posts that each thread has.

The Event Listener

The next step to building the behavior is to write a record event listener that will be responsible for keeping the count up to date when we insert new records, delete a record or batch DQL delete records:

class CountCache extends Doctrine_Template
{
  // ...
 
  public function setTableDefinition()
  {
    // ...
 
    $this->addListener(new CountCacheListener($this->_options));
  }
}

Before we go any further we need to define the CountCacheListener class that extends Doctrine_Record_Listener. It accepts an array of options that are simply forwarded to the listener from the template:

// lib/model/count_cache/CountCacheListener.class.php
 
class CountCacheListener extends Doctrine_Record_Listener
{
  protected $_options;
 
  public function __construct(array $options)
  {
    $this->_options = $options;
  }
}

Now we must utilize the following events in order to keep our counts up to date:

  • postInsert(): Increments the count when a new object is inserted;

  • postDelete(): Decrements the count when a object is deleted;

  • preDqlDelete(): Decrements the counts when records are deleted through a DQL delete.

First let's define the postInsert() method:

class CountCacheListener extends Doctrine_Record_Listener
{
  // ...
 
  public function postInsert(Doctrine_Event $event)
  {
    $invoker = $event->getInvoker();
    foreach ($this->_options['relations'] as $relation => $options)
    {
      $table = Doctrine::getTable($options['className']);
      $relation = $table->getRelation($options['foreignAlias']);
 
      $table
        ->createQuery()
        ->update()
        ->set($options['columnName'], $options['columnName'].' + 1')
        ->where($relation['local'].' = ?', $invoker->$relation['foreign'])
        ->execute();
    }
  }
}

The above code will increment the counts by one for all the configured relationships by issuing a DQL UPDATE query when a new object like below is inserted:

$post = new Post();
$post->thread_id = 1;
$post->body = 'body of the post';
$post->save();

The Thread with an id of 1 will get the num_posts column incremented by 1.

Now that the counts are being incremented when new objects are inserted, we need to handle when objects are deleted and decrement the counts. We will do this by implementing the postDelete() method:

class CountCacheListener extends Doctrine_Record_Listener
{
  // ...
 
  public function postDelete(Doctrine_Event $event)
  {
    $invoker = $event->getInvoker();
    foreach ($this->_options['relations'] as $relation => $options)
    {
      $table = Doctrine::getTable($options['className']);
      $relation = $table->getRelation($options['foreignAlias']);
 
      $table
        ->createQuery()
        ->update()
        ->set($options['columnName'], $options['columnName'].' - 1')
        ->where($relation['local'].' = ?', $invoker->$relation['foreign'])
        ->execute();
    }
  }
}

The above postDelete() method is almost identical to the postInsert() the only difference is we decrement the num_posts column by 1 instead of incrementing it. It handles the following code if we were to delete the $post record we saved previously:

$post->delete();

The last piece to the puzzle is to handle when records are deleted using a DQL update. We can solve this by using the preDqlDelete() method:

class CountCacheListener extends Doctrine_Record_Listener
{
  // ...
 
  public function preDqlDelete(Doctrine_Event $event)
  {
    foreach ($this->_options['relations'] as $relation => $options)
    {
      $table = Doctrine::getTable($options['className']);
      $relation = $table->getRelation($options['foreignAlias']);
 
      $q = clone $event->getQuery();
      $q->select($relation['foreign']);
      $ids = $q->execute(array(), Doctrine::HYDRATE_NONE);
 
      foreach ($ids as $id)
      {
        $id = $id[0];
 
        $table
          ->createQuery()
          ->update()
          ->set($options['columnName'], $options['columnName'].' - 1')
          ->where($relation['local'].' = ?', $id)
          ->execute();
      }
    }
  }
}

The above code clones the DQL DELETE query and transforms it to a SELECT which allows us to retrieve the IDs that will be deleted so that we can update the counts of those records that were deleted.

Now we have the following scenario taken care of and the counts will be decremented if we were to do the following:

Doctrine::getTable('Post')
  ->createQuery()
  ->delete()
  ->where('id = ?', 1)
  ->execute();

Or even if we were to delete multiple records the counts would still be decremented properly:

Doctrine::getTable('Post')
  ->createQuery()
  ->delete()
  ->where('body LIKE ?', '%cool%')
  ->execute();

note

In order for the preDqlDelete() method to be invoked you must enable an attribute. The DQL callbacks are off by default due to them costing a little extra. So if you want to use them, you must enable them.

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

That's it! The behavior is finished. The last thing we'll do is test it out a bit.

Testing

Now that we have the code implemented, let's give it a test run with some sample data fixtures:

# data/fixtures/data.yml
 
Thread:
  thread1:
    title: Test Thread
    Posts:
      post1:
        body: This is the body of my test thread
      post2:
        body: This is really cool
      post3:
        body: Ya it is pretty cool

Now, build everything again and load the data fixtures:

$ php symfony doctrine:build --all --and-load

Now everything is built and the data fixtures are loaded; so let's run a test to see if the counts have been kept up to date:

$ php symfony doctrine:dql "FROM Thread t, t.Posts p"
doctrine - executing: "FROM Thread t, t.Posts p" ()
doctrine -   id: '1'
doctrine -   title: 'Test Thread'
doctrine -   num_posts: '3'
doctrine -   Posts:
doctrine -     -
doctrine -       id: '1'
doctrine -       thread_id: '1'
doctrine -       body: 'This is the body of my test thread'
doctrine -     -
doctrine -       id: '2'
doctrine -       thread_id: '1'
doctrine -       body: 'This is really cool'
doctrine -     -
doctrine -       id: '3'
doctrine -       thread_id: '1'
doctrine -       body: 'Ya it is pretty cool'

You will see the Thread model has a num_posts column, whose value is three. If we were to delete one of the posts with the following code it will decrement the count for you:

$post = Doctrine_Core::getTable('Post')->find(1);
$post->delete();

You will see that the record is deleted and the count is updated:

$ php symfony doctrine:dql "FROM Thread t, t.Posts p"
doctrine - executing: "FROM Thread t, t.Posts p" ()
doctrine -   id: '1'
doctrine -   title: 'Test Thread'
doctrine -   num_posts: '2'
doctrine -   Posts:
doctrine -     -
doctrine -       id: '2'
doctrine -       thread_id: '1'
doctrine -       body: 'This is really cool'
doctrine -     -
doctrine -       id: '3'
doctrine -       thread_id: '1'
doctrine -       body: 'Ya it is pretty cool'

This even works if we were to batch delete the remaining two records with a DQL delete query:

Doctrine_Core::getTable('Post')
  ->createQuery()
  ->delete()
  ->where('body LIKE ?', '%cool%')
  ->execute();

Now we've deleted all the related posts and the num_posts should be zero:

$ php symfony doctrine:dql "FROM Thread t, t.Posts p"
doctrine - executing: "FROM Thread t, t.Posts p" ()
doctrine -   id: '1'
doctrine -   title: 'Test Thread'
doctrine -   num_posts: '0'
doctrine -   Posts: {  }

That is it! I hope this article was both useful in the sense that you learned something about behaviors and the behavior itself is also useful to you!

Using Doctrine Result Caching

In heavily trafficked web applications it is a common need to cache information to save your CPU resources. With the latest Doctrine 1.2 we have made a lot of improvements to the result set caching that gives you much more control over deleting cache entries from the cache drivers. Previously it was not possible to specify the cache key used to store the cache entry so you couldn't really identify the cache entry in order to delete it.

In this section we will show you a simple example of how you can utilize result set caching to cache all your user related queries as well as using events to make sure they are properly cleared when some data is changed.

Our Schema

For this example, let's use the following schema:

# config/doctrine/schema.yml
User:
  columns:
    username:
      type: string(255)
      notnull: true
      unique: true
    password:
      type: string(255)
      notnull: true

Now let's build everything from that schema with the following command:

$ php symfony doctrine:build --all

Once you do that, you should have the following User class generated for you:

// lib/model/doctrine/User.class.php
/**
 * User
 *
 * This class has been auto-generated by the Doctrine ORM Framework
 *
 * @package    ##PACKAGE##
 * @subpackage ##SUBPACKAGE##
 * @author     ##NAME## <##EMAIL##>
 * @version    SVN: $Id: Builder.php 6508 2009-10-14 06:28:49Z jwage $
 */
class User extends BaseUser
{
}

Later in the article you will need to add some code to this class so make note of it.

Configuring Result Cache

In order to use the result cache we need to configure a cache driver for the queries to use. This can be done by setting the ATTR_RESULT_CACHE attribute. We will use the APC cache driver as it is the best choice for production. If you do not have APC available, you can use the Doctrine_Cache_Db or Doctrine_Cache_Array driver for testing purposes.

We can set this attribute in our ProjectConfiguration class. Define a configureDoctrine() method:

// config/ProjectConfiguration.class.php
 
// ...
class ProjectConfiguration extends sfProjectConfiguration
{
  // ...
 
  public function configureDoctrine(Doctrine_Manager $manager)
  {
    $manager->setAttribute(Doctrine_Core::ATTR_RESULT_CACHE, new Doctrine_Cache_Apc());
  }
}

Now that we have the result cache driver configured, we can begin to actually use this driver to cache the result sets of the queries.

Sample Queries

Now imagine in your application you have a bunch of user related queries and you want to clear them whenever some user data is changed.

Here is a simple query that we might use to render a list of users sorted alphabetically:

$q = Doctrine_Core::getTable('User')
    ->createQuery('u')
    ->orderBy('u.username ASC');

Now, we can turn caching on for that query by using the useResultCache() method:

$q->useResultCache(true, 3600, 'users_index');

note

Notice the third argument. This is the key that will be used to store the cache entry for the results in the cache driver. This allows us to easily identify that query and delete it from the cache driver.

Now when we execute the query it will query the database for the results and store them in the cache driver under the key named users_index and any subsequent requests will get the information from the cache driver instead of asking the database:

$users = $q->execute();

note

Not only does this save processing on your database server, it also bypasses the entire hydration process as Doctrine stores the hydrated data. This means that it will relieve some processing on your web server as well.

Now if we check in the cache driver, you will see that there is an entry named users_index:

if ($cacheDriver->contains('users_index'))
{
  echo 'cache exists';
}
else
{
  echo 'cache does not exist';
}

Deleting Cache

Now that the query is cached, we need to learn a bit about how we can delete that cache. We can delete it manually using the cache driver API or we can utilize some events to automatically clear the cache entry when a user is inserted or modified.

Cache Driver API

First we will just demonstrate the raw API of the cache driver before we implement it in an event.

tip

To get access to the result cache driver instance you can get it from the Doctrine_Manager class instance.

$cacheDriver = $manager->getAttribute(Doctrine_Core::ATTR_RESULT_CACHE);

If you don't already have access to the $manager variable already you can retrieve the instance with the following code.

$manager = Doctrine_Manager::getInstance();

Now we can begin to use the API to delete our cache entries:

$cacheDriver->delete('users_index');

You probably have more than one query prefixed with users_ and it would make sense to delete the result cache for all of them. In this case, the delete() method by itself will not work. For this we have a method named deleteByPrefix(), which allows us to delete any cache entry that contains the given prefix. Here is an example:

$cacheDriver->deleteByPrefix('users_');

We have a few other convenient methods we can use to delete cache entries if the deleteByPrefix() is not sufficient for you:

  • deleteBySuffix($suffix): Deletes cache entries that have the passed suffix;

  • deleteByRegexp($regex): Deletes cache entries that match the passed regular expression;

  • deleteAll(): Deletes all cache entries.

Deleting with Events

The ideal way to clear the cache would be to automatically clear it whenever some user data is modified. We can do this by implementing a postSave() event in our User model class definition.

Remember the User class we talked about earlier? Now we need to add some code to it so open the class in your favorite editor and add the following postSave() method:

// lib/model/doctrine/User.class.php
 
class User extends BaseUser
{
  // ...
 
  public function postSave($event)
  {
    $cacheDriver = $this->getTable()->getAttribute(Doctrine_Core::ATTR_RESULT_CACHE);
    $cacheDriver->deleteByPrefix('users_');
  }
}

Now if we were to update a user or insert a new user it would clear the cache for all the user related queries:

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

The next time the queries are invoked it will see the cache does not exist and fetch the data fresh from the database and cache it again for subsequent requests.

While this example is very simple it should demonstrate pretty well how you can use these features to implement fine grained caching on your Doctrine queries.

Writing a Doctrine Hydrator

One of the key features of Doctrine is the ability to transform a Doctrine_Query object to the various result set structures. This is the job of the Doctrine hydrators and up until Doctrine 1.2, the hydrators were all hardcoded and not open for developers to write custom ones. Now that this has changed it is possible to write a custom hydrator and create whatever data structure that is desired from the data the database gives you back when executing a Doctrine_Query instance.

In this example we will build a hydrator that will be extremely simple and easy to understand, yet very useful. It will allow you to select two columns and hydrate the data to a flat array where the first selected column is the key and the second select column is the value.

The Schema and Fixtures

To get started first we need a simple schema to run our tests with. We will just use a simple User model:

# config/doctrine/schema.yml
User:
  columns:
    username: string(255)
    is_active: string(255)

We will also need some data fixtures to test against, so copy the fixtures from below:

# data/fixtures/data.yml
User:
  user1:
    username: jwage
    password: changeme
    is_active: 1
  user2:
    username: jonwage
    password: changeme
    is_active: 0

Now build everything with the following command:

$ php symfony doctrine:build --all --and-load

Writing the Hydrator

To write a hydrator all we need to do is write a new class which extends Doctrine_Hydrator_Abstract and must implement a hydrateResultSet($stmt) method. It receives the PDOStatement instance used to execute the query. We can then use that statement to get the raw results of the query from PDO then transform that to our own structure.

Let's create a new class named KeyValuePairHydrator and place it in the lib/ directory so that symfony can autoload it:

// lib/KeyValuePairHydrator.class.php
class KeyValuePairHydrator extends Doctrine_Hydrator_Abstract
{
  public function hydrateResultSet($stmt)
  {
    return $stmt->fetchAll(Doctrine_Core::FETCH_NUM);
  }
}

The above code as it is now would just return the data exactly as it is from PDO. This isn't quite what we want. We want to transform that data to our own key => value pair structure. So let's modify the hydrateResultSet() method a little bit to do what we want:

// lib/KeyValuePairHydrator.class.php
class KeyValuePairHydrator extends Doctrine_Hydrator_Abstract
{
  public function hydrateResultSet($stmt)
  {
    $results = $stmt->fetchAll(Doctrine_Core::FETCH_NUM);
    $array = array();
    foreach ($results as $result)
    {
      $array[$result[0]] = $result[1];
    }
 
    return $array;
  }
}

Well that was easy! The hydrator code is finished and it does exactly what we want so let's test it!

Using the Hydrator

To use and test the hydrator we first need to register it with Doctrine so that when we execute some queries, Doctrine is aware of the hydrator class we have written.

To do this, register it on the Doctrine_Manager instance in the ProjectConfiguration:

// config/ProjectConfiguration.class.php
 
// ...
class ProjectConfiguration extends sfProjectConfiguration
{
  // ...
 
  public function configureDoctrine(Doctrine_Manager $manager)
  {
    $manager->registerHydrator('key_value_pair', 'KeyValuePairHydrator');
  }
}

Now that we have the hydrator registered, we can make use of it with Doctrine_Query instances. Here is an example:

$q = Doctrine_Core::getTable('User')
  ->createQuery('u')
  ->select('u.username, u.is_active');
 
$results = $q->execute(array(), 'key_value_pair');
print_r($results);

Executing the above query with the data fixtures we defined above would result in the following:

Array
(
    [jwage] => 1
    [jonwage] => 0
)

Well that is it! Pretty simple huh? I hope this will be useful for you and as a result the community gets some awesome new hydrators contributed.


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