php Collection类的设计

用。net开发已经很多年了，最近接触到php，发现php也很好玩。不过发现它里面没有集合Collection类，只有数组，并且数组很强。这里我用数组来包装成一个集合Collection，代码如下：

class Collection{private $_members=array();public  function addItem($obj,$key=null){if($key){if(isset($this->_members[$key])){throw  new exception("Key \"$key\" already in use!");}else{$this->_members[$key]=$obj;}}else{$this->_members[]=$obj;}}public function removeItem($key){if(isset($this->_members[$key])){unset($this->_members[$key]);}else{throw new exception("Invalid Key \"$key\"!");}}public function getItem($key){if(isset($this->_members[$key])){return $this->_members[$key];}else{throw new  exception("Invalid Key \"$key\"!");}}public function Keys(){return array_keys($this->_members);}public function legth(){return sizeof($this->_members);}public function exists($key){return (isset($this->_members[$key]));}
}

现在我们来测试一下这个集合是否好用。

我们首先建立一个集合元素类Course：

class  Course
{private $_id;private $_courseCode;private $_name;public function __construct($id,$courseCode,$name){$this->_id=$id;$this->_courseCode=$courseCode;$this->_name=$name;}public function getName(){return $this->_name;}public function getID(){return $this->_id;}public function getCourseCode(){return $this->_courseCode;}public function __toString(){return $this->_name;}
}

测试代码如下：
$courses=new Collection();
$courses->addItem(new Course(1, "001", "语文"),1);
$courses->addItem(new Course(2, "002", "数学"),2);
$obj=$courses->getItem(1);
print $obj;
我想这个集合类应该可以满足我们平日开发的需求了吧。
可是我们现在。net里面有个对象延迟加载，举个例子来说吧，假如现在有Student这个对象，它应该有很多Course，但是我们希望在访问Course之前Course是不会加载的。也就是说在实例化Student的时候Course个数为0，当我们需要Course的时候它才真正从数据库读取相应数据。就是需要我们把Collection做成惰性实例化。
修改后的Collection代码如下：

class Collection {private $_members = array();    //collection members
private $_onload;               //holder for callback function
private $_isLoaded = false;     //flag that indicates whether the callback//has been invoked
public function addItem($obj, $key = null) {$this->_checkCallback();      //_checkCallback is defined a little later
        if($key) {if(isset($this->_members[$key])) {throw new KeyInUseException("Key \"$key\" already in use!");} else {$this->_members[$key] = $obj;}} else {$this->_members[] = $obj;}}public function removeItem($key) {$this->_checkCallback();if(isset($this->_members[$key])) {unset($this->_members[$key]);} else {throw new KeyInvalidException("Invalid key \"$key\"!");}  }public function getItem($key) {$this->_checkCallback();if(isset($this->_members[$key])) {return $this->_members[$key];} else {throw new KeyInvalidException("Invalid key \"$key\"!");}}public function keys() {$this->_checkCallback();return array_keys($this->_members);}public function length() {$this->_checkCallback();return sizeof($this->_members);}public function exists($key) {$this->_checkCallback();return (isset($this->_members[$key]));}/*** Use this method to define a function to be * invoked prior to accessing the collection.  * The function should take a collection as a * its sole parameter.*/public function setLoadCallback($functionName, $objOrClass = null) {if($objOrClass) {$callback = array($objOrClass, $functionName);} else {$callback = $functionName;}//make sure the function/method is validif(!is_callable($callback, false, $callableName)) {throw new Exception("$callableName is not callable " . "as a parameter to onload");return false;}$this->_onload = $callback;}/*** Check to see if a callback has been defined and if so,* whether or not it has already been called.  If not,* invoke the callback function.*/private function _checkCallback() {if(isset($this->_onload) && !$this->_isLoaded) {$this->_isLoaded = true;call_user_func($this->_onload, $this);}}
}

所需的Student如下：

class CourseCollection extends Collection {public function addItem(Course $obj,$key=null) {parent::addItem($obj,$key);}
}
class Student{private $_id;private $_name;public $course;public	function __construct($id,$name){$this->_id=$id;$this->_name=$name;$this->course=new CourseCollection();$this->course->setLoadCallback('loadCourses',$this);}public function getName(){return $this->_name;}public function getID(){return $this->_id;}public function __toString(){return $this->_name;}public function loadCourses(Collection $col){$col->addItem(new Course(1, "001", "语文"),1);$col->addItem(new Course(2, "002", "数学"),2);}
}

调用代码如下：

$student=new Student(1, "majiang");
print $student->getName();
print $student->course->getItem(1);