[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 < 0 || $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();}

        \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);}

        \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';}}

        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());}}

        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();}}

        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());}//....}

         例子：

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

        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。