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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