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 implementation 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;
/**
* initialize 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