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HomeBackend DevelopmentPHP TutorialDetailed 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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