Persisting the Decorator Pattern ================================ .. sectionauthor:: Chris Woodford <chris.woodford@gmail.com> This recipe will show you a simple example of how you can use Doctrine 2 to persist an implementaton of the `Decorator Pattern <http://en.wikipedia.org/wiki/Decorator_pattern>`_ Component --------- The ``Component`` class needs to be persisted, so it's going to be an ``Entity``. As the top of the inheritance hierarchy, it's going to have to define the persistent inheritance. For this example, we will use Single Table Inheritance, but Class Table Inheritance would work as well. In the discriminator map, we will define two concrete subclasses, ``ConcreteComponent`` and ``ConcreteDecorator``. .. code-block:: php <?php namespace Test; /** * @Entity * @InheritanceType("SINGLE_TABLE") * @DiscriminatorColumn(name="discr", type="string") * @DiscriminatorMap({"cc" = "Test\Component\ConcreteComponent", "cd" = "Test\Decorator\ConcreteDecorator"}) */ abstract class Component { /** * @Id @Column(type="integer") * @GeneratedValue(strategy="AUTO") */ protected $id; /** @Column(type="string", nullable="true") */ protected $name; /** * Get id * @return integer $id */ public function getId() { return $this->id; } /** * Set name * @param string $name */ public function setName($name) { $this->name = $name; } /** * Get name * @return string $name */ public function getName() { return $this->name; } } ConcreteComponent ----------------- The ``ConcreteComponent`` class is pretty simple and doesn't do much more than extend the abstract ``Component`` class (only for the purpose of keeping this example simple). .. code-block:: php <?php namespace Test\Component; use Test\Component; /** @Entity */ class ConcreteComponent extends Component {} Decorator --------- The ``Decorator`` class doesn't need to be persisted, but it does need to define an association with a persisted ``Entity``. We can use a ``MappedSuperclass`` for this. .. code-block:: php <?php namespace Test; /** @MappedSuperclass */ abstract class Decorator extends Component { /** * @OneToOne(targetEntity="Test\Component", cascade={"all"}) * @JoinColumn(name="decorates", referencedColumnName="id") */ protected $decorates; /** * intialize the decorator * @param Component $c */ public function __construct(Component $c) { $this->setDecorates($c); } /** * (non-PHPdoc) * @see Test.Component::getName() */ public function getName() { return 'Decorated ' . $this->getDecorates()->getName(); } /** * the component being decorated * @return Component */ protected function getDecorates() { return $this->decorates; } /** * sets the component being decorated * @param Component $c */ protected function setDecorates(Component $c) { $this->decorates = $c; } } All operations on the ``Decorator`` (i.e. persist, remove, etc) will cascade from the ``Decorator`` to the ``Component``. This means that when we persist a ``Decorator``, Doctrine will take care of persisting the chain of decorated objects for us. A ``Decorator`` can be treated exactly as a ``Component`` when it comes time to persisting it. The ``Decorator's`` constructor accepts an instance of a ``Component``, as defined by the ``Decorator`` pattern. The setDecorates/getDecorates methods have been defined as protected to hide the fact that a ``Decorator`` is decorating a ``Component`` and keeps the ``Component`` interface and the ``Decorator`` interface identical. To illustrate the intended result of the ``Decorator`` pattern, the getName() method has been overridden to append a string to the ``Component's`` getName() method. ConcreteDecorator ----------------- The final class required to complete a simple implementation of the Decorator pattern is the ``ConcreteDecorator``. In order to further illustrate how the ``Decorator`` can alter data as it moves through the chain of decoration, a new field, "special", has been added to this class. The getName() has been overridden and appends the value of the getSpecial() method to its return value. .. code-block:: php <?php namespace Test\Decorator; use Test\Decorator; /** @Entity */ class ConcreteDecorator extends Decorator { /** @Column(type="string", nullable="true") */ protected $special; /** * Set special * @param string $special */ public function setSpecial($special) { $this->special = $special; } /** * Get special * @return string $special */ public function getSpecial() { return $this->special; } /** * (non-PHPdoc) * @see Test.Component::getName() */ public function getName() { return '[' . $this->getSpecial() . '] ' . parent::getName(); } } Examples -------- Here is an example of how to persist and retrieve your decorated objects .. code-block:: php <?php use Test\Component\ConcreteComponent, Test\Decorator\ConcreteDecorator; // assumes Doctrine 2 is configured and an instance of // an EntityManager is available as $em // create a new concrete component $c = new ConcreteComponent(); $c->setName('Test Component 1'); $em->persist($c); // assigned unique ID = 1 // create a new concrete decorator $c = new ConcreteComponent(); $c->setName('Test Component 2'); $d = new ConcreteDecorator($c); $d->setSpecial('Really'); $em->persist($d); // assigns c as unique ID = 2, and d as unique ID = 3 $em->flush(); $c = $em->find('Test\Component', 1); $d = $em->find('Test\Component', 3); echo get_class($c); // prints: Test\Component\ConcreteComponent echo $c->getName(); // prints: Test Component 1 echo get_class($d) // prints: Test\Component\ConcreteDecorator echo $d->getName(); // prints: [Really] Decorated Test Component 2