253 lines
8.5 KiB
ReStructuredText
253 lines
8.5 KiB
ReStructuredText
Strategy-Pattern
|
|
================
|
|
|
|
This recipe will give you a short introduction on how to design
|
|
similar entities without using expensive (i.e. slow) inheritance
|
|
but with not more than \* the well-known strategy pattern \* event
|
|
listeners
|
|
|
|
Scenario / Problem
|
|
------------------
|
|
|
|
Given a Content-Management-System, we probably want to add / edit
|
|
some so-called "blocks" and "panels". What are they for?
|
|
|
|
|
|
- A block might be a registration form, some text content, a table
|
|
with information. A good example might also be a small calendar.
|
|
- A panel is by definition a block that can itself contain blocks.
|
|
A good example for a panel might be a sidebar box: You could easily
|
|
add a small calendar into it.
|
|
|
|
So, in this scenario, when building your CMS, you will surely add
|
|
lots of blocks and panels to your pages and you will find yourself
|
|
highly uncomfortable because of the following:
|
|
|
|
|
|
- Every existing page needs to know about the panels it contains -
|
|
therefore, you'll have an association to your panels. But if you've
|
|
got several types of panels - what do you do? Add an association to
|
|
every panel-type? This wouldn't be flexible. You might be tempted
|
|
to add an AbstractPanelEntity and an AbstractBlockEntity that use
|
|
class inheritance. Your page could then only confer to the
|
|
AbstractPanelType and Doctrine 2 would do the rest for you, i.e.
|
|
load the right entities. But - you'll for sure have lots of panels
|
|
and blocks, and even worse, you'd have to edit the discriminator
|
|
map *manually* every time you or another developer implements a new
|
|
block / entity. This would tear down any effort of modular
|
|
programming.
|
|
|
|
Therefore, we need something thats far more flexible.
|
|
|
|
Solution
|
|
--------
|
|
|
|
The solution itself is pretty easy. We will have one base class
|
|
that will be loaded via the page and that has specific behaviour -
|
|
a Block class might render the front-end and even the backend, for
|
|
example. Now, every block that you'll write might look different or
|
|
need different data - therefore, we'll offer an API to these
|
|
methods but internally, we use a strategy that exactly knows what
|
|
to do.
|
|
|
|
First of all, we need to make sure that we have an interface that
|
|
contains every needed action. Such actions would be rendering the
|
|
front-end or the backend, solving dependencies (blocks that are
|
|
supposed to be placed in the sidebar could refuse to be placed in
|
|
the middle of your page, for example).
|
|
|
|
Such an interface could look like this:
|
|
|
|
|
|
::
|
|
|
|
<?php
|
|
/**
|
|
* This interface defines the basic actions that a block / panel needs to support.
|
|
*
|
|
* Every blockstrategy is *only* responsible for rendering a block and declaring some basic
|
|
* support, but *not* for updating its configuration etc. For this purpose, use controllers
|
|
* and models.
|
|
*/
|
|
interface BlockStrategyInterface {
|
|
/**
|
|
* This could configure your entity
|
|
*/
|
|
public function setConfig(Config\EntityConfig $config);
|
|
|
|
/**
|
|
* Returns the config this strategy is configured with.
|
|
* @return Core\Model\Config\EntityConfig
|
|
*/
|
|
public function getConfig();
|
|
|
|
/**
|
|
* Set the view object.
|
|
* @param \Zend_View_Interface $view
|
|
* @return \Zend_View_Helper_Interface
|
|
*/
|
|
public function setView(\Zend_View_Interface $view);
|
|
|
|
/**
|
|
* @return \Zend_View_Interface
|
|
*/
|
|
public function getView();
|
|
|
|
/**
|
|
* Renders this strategy. This method will be called when the user
|
|
* displays the site.
|
|
*
|
|
* @return string
|
|
*/
|
|
public function renderFrontend();
|
|
|
|
/**
|
|
* Renders the backend of this block. This method will be called when
|
|
* a user tries to reconfigure this block instance.
|
|
*
|
|
* Most of the time, this method will return / output a simple form which in turn
|
|
* calls some controllers.
|
|
*
|
|
* @return string
|
|
*/
|
|
public function renderBackend();
|
|
|
|
/**
|
|
* Returns all possible types of panels this block can be stacked onto
|
|
*
|
|
* @return array
|
|
*/
|
|
public function getRequiredPanelTypes();
|
|
|
|
/**
|
|
* Determines whether a Block is able to use a given type or not
|
|
* @param string $typeName The typename
|
|
* @return boolean
|
|
*/
|
|
public function canUsePanelType($typeName);
|
|
|
|
public function setBlockEntity(AbstractBlock $block);
|
|
|
|
public function getBlockEntity();
|
|
}
|
|
|
|
As you can see, we have a method "setBlockEntity" which ties a potential strategy to an object of type AbstractBlock. This type will simply define the basic behaviour of our blocks and could potentially look something like this:
|
|
|
|
<?php
|
|
/**
|
|
* This is the base class for both Panels and Blocks.
|
|
* It shouldn't be extended by your own blocks - simply write a strategy!
|
|
*/
|
|
abstract class AbstractBlock {
|
|
/**
|
|
* The id of the block item instance
|
|
* This is a doctrine field, so you need to setup generation for it
|
|
* @var integer
|
|
*/
|
|
private $id;
|
|
|
|
// Add code for relation to the parent panel, configuration objects, ....
|
|
|
|
/**
|
|
* This var contains the classname of the strategy
|
|
* that is used for this blockitem. (This string (!) value will be persisted by Doctrine 2)
|
|
*
|
|
* This is a doctrine field, so make sure that you use an @column annotation or setup your
|
|
* yaml or xml files correctly
|
|
* @var string
|
|
*/
|
|
protected $strategyClassName;
|
|
|
|
/**
|
|
* This var contains an instance of $this->blockStrategy. Will not be persisted by Doctrine 2.
|
|
*
|
|
* @var BlockStrategyInterface
|
|
*/
|
|
protected $strategyInstance;
|
|
|
|
/**
|
|
* Returns the strategy that is used for this blockitem.
|
|
*
|
|
* The strategy itself defines how this block can be rendered etc.
|
|
*
|
|
* @return string
|
|
*/
|
|
public function getStrategyClassName() {
|
|
return $this->strategyClassName;
|
|
}
|
|
|
|
/**
|
|
* Returns the instantiated strategy
|
|
*
|
|
* @return BlockStrategyInterface
|
|
*/
|
|
public function getStrategyInstance() {
|
|
return $this->strategyInstance;
|
|
}
|
|
|
|
/**
|
|
* Sets the strategy this block / panel should work as. Make sure that you've used
|
|
* this method before persisting the block!
|
|
*
|
|
* @param BlockStrategyInterface $strategy
|
|
*/
|
|
public function setStrategy(BlockStrategyInterface $strategy) {
|
|
$this->strategyInstance = $strategy;
|
|
$this->strategyClassName = get_class($strategy);
|
|
$strategy->setBlockEntity($this);
|
|
}
|
|
|
|
Now, the important point is that $strategyClassName is a Doctrine 2
|
|
field, i.e. Doctrine will persist this value. This is only the
|
|
class name of your strategy and not an instance!
|
|
|
|
Finishing your strategy pattern, we hook into the Doctrine postLoad
|
|
event and check whether a block has been loaded. If so, you will
|
|
initialize it - i.e. get the strategies classname, create an
|
|
instance of it and set it via setStrategyBlock().
|
|
|
|
This might look like this:
|
|
|
|
::
|
|
|
|
<?php
|
|
use \Doctrine\ORM,
|
|
\Doctrine\Common;
|
|
|
|
/**
|
|
* The BlockStrategyEventListener will initialize a strategy after the
|
|
* block itself was loaded.
|
|
*/
|
|
class BlockStrategyEventListener implements Common\EventSubscriber {
|
|
|
|
protected $view;
|
|
|
|
public function __construct(\Zend_View_Interface $view) {
|
|
$this->view = $view;
|
|
}
|
|
|
|
public function getSubscribedEvents() {
|
|
return array(ORM\Events::postLoad);
|
|
}
|
|
|
|
public function postLoad(ORM\Event\LifecycleEventArgs $args) {
|
|
$blockItem = $args->getEntity();
|
|
|
|
// Both blocks and panels are instances of Block\AbstractBlock
|
|
if ($blockItem instanceof Block\AbstractBlock) {
|
|
$strategy = $blockItem->getStrategyClassName();
|
|
$strategyInstance = new $strategy();
|
|
if (null !== $blockItem->getConfig()) {
|
|
$strategyInstance->setConfig($blockItem->getConfig());
|
|
}
|
|
$strategyInstance->setView($this->view);
|
|
$blockItem->setStrategy($strategyInstance);
|
|
}
|
|
}
|
|
}
|
|
|
|
In this example, even some variables are set - like a view object
|
|
or a specific configuration object.
|
|
|
|
|