[php]Collection跟持久化工厂 -php教程-PHP中文網

[php]Collection和持久化工厂

Mapper类中的findById($id)可以从数据库中取出指定id的一条数据，映射成一个对象返回。很多时候我们需要返回一个数据集合（findAll），那我们就需要一种数据结构来保存这些数据，在需要时映射成对象。既然一条数据映射成一个对象，那么一个数据集合就需要一个对象集合。可以把数据集合和对象集合放在一个类中，这样就方便处理数据到对象的映射了。我们把这个类命名为Collection，为了能更好好的访问集合对象，Collection子类都实现了Iterator接口，使用foreach可以方便访问。

Collection的类结构：

\demo\mapper\Collection：

namespace demo\mapper;

use demo\base\AppException;
use demo\domain\DomainObject;
use demo\mapper\Mapper;

abstract class Collection {
	// 保存数据库取出的行数据
	protected $raws;
	// 保存已映射的对象
	protected $objects = array();
	// 用于$raws[]到$objects的映射
	protected $mapper;
	// 当前指针
	private $pointer = 0;
	// 对象数组总数
	private $total = 0;
	
	/**
	 * @param array $raws 未处理过的数据库数据
	 * @param Mapper $mapper 用于把$raws映射成对象（createObject）
	 */
	public function __construct(array $raws = null, Mapper $mapper = null) {
		if (!is_null($raws) && !is_null($mapper)) {
			$this->raws = $raws;
			$this->total = count($raws);
		}
		
		$this->mapper = $mapper;
	}
	
	/**
	 * 返回指定$num的数据对象
	 * @param int $num
	 */
	public function getRow($num) {
		if ($num = $this->total) {
			return null;
		}
		
		// 延迟加载
		$this->notifyAccess();
		
		if (isset($this->objects[$num])) {
			return $this->objects[$num];
		}
		
		if (isset($this->raws[$num])) {
			$obj = $this->mapper->createObject($this->raws[$num]);
			$this->objects[$num] = $obj;
			return $obj;
		}
		
		return null;
	}
	
	/**
	 * 添加对象
	 * @param DomainObject $obj
	 * @throws AppException
	 */
	public function add(DomainObject $obj) {
		// 类型安全检查
		$targetClass = $this->getTargetClass();
		if (!($obj instanceof $targetClass)) {
			throw new AppException("Object must be {$targetClass}");
		}
		
		// 
		$this->notifyAccess();
		$this->objects[$this->pointer++] = $obj;
	}
	
	public function current() {
		return $this->getRow($this->pointer);
	}
	
	public function next() {
		$obj = $this->getRow($this->pointer);
		if (!is_null($obj)) {
			$this->pointer++;
		}
		
		return $obj;
	}
	
	public function key() {
		return $this->pointer;
	}
	
	public function rewind() {
		$this->pointer = 0;
	}
	
	public function valid() {
		return !is_null($this->current());
	}
	
	/**
	 * 延迟加载
	 */
	protected  function notifyAccess() {
		// 暂时留空
	}
	
	protected abstract function getTargetClass();
}

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\demo\domain：

namespace demo\domain;

use \demo\domain\DomainObject;

interface ClassroomCollection extends \Iterator {
	public function add(DomainObject $obj);
}

interface StudentCollection extends \Iterator {
	public function add(DomainObject $obj);
}

interface ScoreCollection extends \Iterator {
	public function add(DomainObject $obj);
}

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\demo\mapper：

namespace demo\mapper;

class ClassroomCollection extends Collection 
		implements \demo\domain\ClassroomCollection {
	
	protected function getTargetClass() {
		return '\demo\domain\Classroom';
	}
}

class StudentCollection extends Collection 
		implements \demo\domain\StudentCollection {
	
	protected function getTargetClass() {
		return '\demo\domain\Student';
	}
}

class ScoreCollection extends Collection 
		implements \demo\domain\ScoreCollection {

	protected function getTargetClass() {
		return '\demo\domain\Score';
	}
}

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为什么需要为domain包还需要一个Collection接口呢？因为domain包需要用到Collection来保存数据，为了让domain包不依赖于mapper包的Collection，所以创建了一个接口。而\demo\domain\mapper\Collection则会实现这个接口。

现在的结构开始有点复杂了，为了能管理好Mapper和Collection的具体子类，我们可以使用抽象工厂来管理对象的创建。来看看类图：

\demo\mapper\PersistanceFatory

namespace demo\mapper;

/**
 * 持久化工厂
 */
abstract class PersistanceFactory {
	
	public static function getFactory($targetClass) {
		switch ($targetClass) {
			case '\demo\domain\Classroom':
				return new ClassroomPersistanceFactory();
				
			case '\demo\domain\Student':
				return new StudentPersistanceFactory();
				
			case '\demo\domain\Score':
				return new ScorePersistanceFactory();
		}
	}
	
	public abstract function getMapper();
	
	public abstract function getCollection(array $raws = null);
}

class ClassroomPersistanceFactory extends PersistanceFactory {
	public function getMapper() {
		return new ClassroomMapper();
	}
	
	public function getCollection(array $raws = null) {
		return new ClassroomCollection($raws, $this->getMapper());
	}
}

class StudentPersistanceFactory extends PersistanceFactory {
	public function getMapper() {
		return new StudentMapper();
	}
	
	public function getCollection(array $raws = null) {
		return new StudentCollection($raws, $this->getMapper());
	}
}

class ScorePersistanceFactory extends PersistanceFactory {
	public function getMapper() {
		return new ScoreMapper();
	}
	
	public function getCollection(array $raws = null) {
		return new ScoreCollection($raws, $this->getMapper());
	}
}

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使用这样的工厂模式可以很方便地创建指定的Mapper和Collection子类了，同时这种方式也可以方便以后新功能的添加。

domain包中同样需要Collection对象，但需要注意和mapper中的Collection分离开来。我们可以在domain包中创一个HelperFactory类来当做domain访问mapper的桥梁。

namespace demo\domain;

use demo\mapper\PersistanceFactory;

class HelperFactory {
	
	public static function getCollection($targetClass) {
		$fact = PersistanceFactory::getFactory($targetClass);
		return $fact->getCollection();
	}
	
	public static function getFinder($targetClass) {
		$fact = PersistanceFactory::getFactory($targetClass);
		return $fact->getMapper();	
	}
}

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这样就把domain包和mapper包分离开来了。

Collection有了，那么就来实现Mapper的findAll()吧。

namespace demo\mapper;

use demo\base\AppException;
use \demo\base\ApplicationRegistry;

/**
 * Mapper
 */
abstract  class Mapper {
	
	//...
	
	/**
	 * 返回Collection
	 */
	public function findAll() {
		$pStmt = $this->getSelectAllStmt();
		$pStmt->execute(array());
		$raws = $pStmt->fetchAll(\PDO::FETCH_ASSOC);
		$collection = $this->getCollection($raws);
		
		return $collection;
	}
	
	/**
	 * 返回子类Collection
	 * @param array $raw
	 */
	public function getCollection(array $raws) {
		return $this->getFactory()->getCollection($raws);
	}
	
	/**
	 * 返回子类持久化工厂对象
	 */
	public function getFactory() {
		return PersistanceFactory::getFactory($this->getTargetClass());		
	}
	
	//....
}

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例子：

$fact = PersistanceFactory::getFactory('\demo\domain\Classroom');
$mapper = $fact->getMapper();
$classrooms = $mapper->findAll();
foreach ($classrooms as $elem) {
	var_dump($elem);
}

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Colletion能方便管理$raws[]到$objects[]的映射。
PersistanceFactory能管理好mapper包中类对象的创建。
HelperFactory把mapper包和domain包分离开来。