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淺析PHP中Collection 類的設(shè)計(jì)

更新時(shí)間：2013年06月21日 09:13:04 作者：

本篇文章是對(duì)PHP中Collection 類進(jìn)行了詳細(xì)的分析介紹，需要的朋友參考下

用.net開(kāi)發(fā)已經(jīng)很多年了，最近接觸到php，發(fā)現(xiàn)php也很好玩。不過(guò)發(fā)現(xiàn)它里面沒(méi)有集合Collection類，只有數(shù)組，并且數(shù)組很強(qiáng)。這里我用數(shù)組來(lái)包裝成一個(gè)集合Collection，代碼如下：

復(fù)制代碼代碼如下:

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])); 
    } 
}

現(xiàn)在我們來(lái)測(cè)試一下這個(gè)集合是否好用。
我們首先建立一個(gè)集合元素類Course：

復(fù)制代碼代碼如下:

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; 
    } 
}

測(cè)試代碼如下：
$courses=new Collection();
$courses->addItem(new Course(1, "001", "語(yǔ)文"),1);
$courses->addItem(new Course(2, "002", "數(shù)學(xué)"),2);
$obj=$courses->getItem(1);
print $obj;
我想這個(gè)集合類應(yīng)該可以滿足我們平日開(kāi)發(fā)的需求了吧。
可是我們現(xiàn)在。net里面有個(gè)對(duì)象延遲加載，舉個(gè)例子來(lái)說(shuō)吧，假如現(xiàn)在有Student這個(gè)對(duì)象，它應(yīng)該有很多Course，但是我們希望在訪問(wèn)Course之前Course是不會(huì)加載的。也就是說(shuō)在實(shí)例化Student的時(shí)候Course個(gè)數(shù)為0，當(dāng)我們需要Course的時(shí)候它才真正從數(shù)據(jù)庫(kù)讀取相應(yīng)數(shù)據(jù)。就是需要我們把Collection做成惰性實(shí)例化。
修改后的Collection代碼如下：

復(fù)制代碼代碼如下:

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：

復(fù)制代碼代碼如下:

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", "語(yǔ)文"),1); 
        $col->addItem(new Course(2, "002", "數(shù)學(xué)"),2); 
    } 
}