Detailed explanation of PHP object-oriented identity mapping
/*标识映射在数据映射器的基础上增加了标识映射类,主要功能是保存已经创建好的对象,在需要的时候可以直接获取而不是重复创建造成系统性能的下降。 在数据映射器基础上还增加了部分调用标识映射类的方法,示例代码如下:*/namespace woo\domain;//标识映射类class ObjectWatcher{ private $all = array(); //存放对象的小仓库private static $instance; //单例private function __construct (){} static function instance(){if(!self::$instance){ self::$instance = new ObjectWatcher(); }return self::$instance; } //获取一个唯一的标识,这里采用了领域类类名+ID的方式创建一个唯一标识,避免多个数据库表调用这个类时出现ID重复的问题function globalKey(DomainObject $obj){$key = get_class($obj) . "." . $obj->getId();return $key; } //添加对象static function add(DomainObject $obj){$inst = self::instance();$inst->all[$inst->globalKey($obj)] = $obj; } //获取对象static function exists($classname,$id){$inst = self::instance();$key = "$classname.$id";if(isset($inst->all[$key]){return $inst->all[$key]; }return null; } } namespace woo\mapper;abstract class Mapper{ //抽象基类abstract static $PDO; //操作数据库的pdo对象function __construct (){if(!isset(self::$PDO){$dsn = \woo\base\ApplicationRegistry::getDSN();if(is_null($dsn)){throw new \woo\base\AppException("no dns"); } self::$PDO = new \PDO($dsn); self::$PDO->setAttribute(\PDO::ATTR_ERRMODE,\PDO::ERRMODE_EXCEPTION); } } //数据映射器基础上新增的方法以下会简称新增,这里的作用的是获取对象而不是查询数据库并重复创建对象 //(对比一下原数据映射器的相关代码即可了解)private function getFroMap($id){return \woo\domain\ObjectWatcher::exists($this->targetClass(),$id); } //新增,这里的作用的是将创建的对象保存起来private function addToMap(\woo\domain\DomainObject $obj){//////return \woo\domain\ObjectWatcher::add($obj); } //对比原数据映射器的代码,便发现它不是直接创建对象而是首先在标识映射类中查找,找不到才调用的 //子类的方法创建并插入到标识映射类,下面的find方法也遵循了这一原则function createObject($array){ $old = $this->getFromMap($array['id']); //新增if($old){return $old} //新增$obj = $this->doCreateObject($array); //在子类中实现$this->addToMap($obj); //新增return $obj; } // function find($id){ //通过ID从数据库中获取一条数据并创建为对象 $old = $this->getFromMap($id); //新增if($old){return $old} //新增$this->selectStmt()->execute(array($id));$array= $this->selectStmt()->fetch();$this->selectStmt()->closeCursor();if(!is_array($array)){return null; }if(!isset($array['id'])){return null; }$object = $this->createObject($array);$this->addToMap($object); //新增return $object; } function insert(\woo\domain\DomainObject $obj){ //将对象数据插入数据库$this->doInsert($obj);$this->addToMap($obj); //新增 } //需要在子类中实现的各抽象方法abstract function targetClass();//////abstract function update(\woo\domain\DomainObject $objet);protected abstract function doCreateObject(array $array);protected abstract function selectStmt();protected abstract function doInsert(\woo\domain\DomainObject $object); }class SpaceMapper extends Mapper {//其他代码在数据映射器一文中已有实现这里略过 //............. //类名,在标识映射类中生成唯一标识用的protected function targetClass(){return "woo\\domain\\Space"; } }
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