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 = $functionName;    }        //make sure the function/method is valid    if(!is_callable($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);