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：

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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：

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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：

+ View Code?

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);