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[Doctrine 1.2 extension] allow relations to records of multiple types

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README.md

LooseCoupling

LooseCoupling is a Doctrine 1 extension to allow relations to records of multiple types without foreign key constraints.

LooseCoupling provides a Doctrine behaviour and two Hydrator modes to be used in combination.

Usage

To use this extension on any of your models you have to apply the behaviour to it.

class YourModel extends Doctrine_Record
{
  public function setTableDefinition()
  {
    ...
  }

  public function setUp()
  {
    $looselycoupleable = new LooselyCoupleable();
    $this->actAs($looselycoupleable);
  }
}

Here the same as above using a schema.yml definition.

YourModel:
  actAs: [LooselyCoupleable]
  columns:
    ...

The behaviour will add the two columns obj_type and obj_pk to your model and database table and provides two delegate methods getObject() and setObject(Doctrine_Record $object).

id ... obj_type obj_pk
1 ... Image 1
2 ... Image 2
3 ... Article 1

The only limitation is that only single column primary key models can be used!

The above table can be illustrated like this.

LooseCoupling example illustration

The template will also provide a virtual column Object.

You can now add any Doctrine_Record to YourModel as the following code demonstrates.

$yourModel->Object = $image;
// is the same as
$yourModel->obj_type = get_class($image);
$yourModel->obj_pk = $image->id;

You can also access the loosely related Object.

echo $yourModel->Object;
// will call the toString() method of the related record instance ($image in the case above)

You can also access the loosely related Object.

echo $yourModel->Object;
// will call the toString() method of the related record instance ($image in the case above)

The behaviour implements lazy loading for the Object property querying the database when you access the Object for the first time.

Of course you don't want and extra query each time you access the Object property for the first time. This can be quite costly especially when doing it inside a loop.

$yourModels = Doctrine_Core::getTable('YourModel')->findAll();
foreach($yourModels as $yourModel)
{
  echo $yourModel->Object; // can be Image, Article, whatever, ..
}

The above example will issue 1 query to the database to fetch all YourModel instances and 1 additional query per instance. Which makes 1 + N queries where N is the number of records in the YourModel table.

This is where the two new hydrator modes come into play. Rewriting the above example using these new modes we get this.

Doctrine_Manager::getInstance()->registerHydrator('ArrayCoupled', 'Doctrine_Hydrator_ArrayCoupled');
Doctrine_Manager::getInstance()->registerHydrator('RecordCoupled', 'Doctrine_Hydrator_RecordCoupled');

$yourModels = Doctrine_Core::getTable('YourModel')->findAll('RecordCoupled');
foreach($yourModels as $yourModel)
{
  echo $yourModel->Object; // can be Image, Article, whatever, ..
}

By using the RecordCoupled hydrator the number of queries gets reduced to the minimum of 1 query to the database to fetch all YourModel instances and 1 additional query per type of related models. Which makes 1 + M queries where M is the number of different models related in the YourModel table. For the table shown above this would be 3 instead of 4 queries.

There are two hydrator modes available Doctrine_Hydrator_ArrayCoupled and Doctrine_Hydrator_RecordCoupled which can replace the default Doctrine_Core::HYDRATE_ARRAY and Doctrine_Core::HYDRATE_RECORD.

Even when YourModel is only considered by i.e. a leftJoin() in one of your queries its loosely coupled relations will be made available.

A complementary behaviour for the object

Looking at the above example it might be desireable to be able to fetch all instances of YourModel for an Article that have a loose coupling to it.

However you can not simply define a relation as it would not filter out those that share the correct primary key but not the correct model. For this there is a complementary behaviour called LooselyCoupled.

class Article extends Doctrine_Record
{
  public function setTableDefinition()
  {
    ...
  }

  public function setUp()
  {
    $looselycoupled = new LooselyCoupled(array('Models' => 'YourModel'));
    $this->actAs($looselycoupled);
  }
}

Where Models is the alias and YourModel refers to the related model name. Here the same as above using a schema.yml definition.

YourModel:
  actAs:
    LooselyCoupled:
      Models: YourModel
  columns:
    ...

This behaviour will add a listener that will extend the anty LEFT JOIN to the YourModel table by a filter for the correct obj_type.

You can now access all YourModel instances that are loosely coupled to an article like in the following example.

$ones = Doctrine_Core::getTable('Article')
  ->createQuery('a')
  ->leftJoin('a.Models m')
  ->execute();

This passive behaviour will also ensure that loosely coupled objects get deleted when the origin - in this case Article - is deleted.

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