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HomeBackend DevelopmentPHP TutorialIntroduction to object-oriented identity mapping in PHP

Introduction to object-oriented identity mapping in PHP

Aug 12, 2017 pm 04:42 PM
phpintroducemapping

下面小编就为大家带来一篇老生常谈PHP面向对象之标识映射。小编觉得挺不错的。现在就分享给大家,也给大家做个参考。一起跟随小编过来看看吧

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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