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也没好玩。不过发现它里面没有集合类，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 $course;publicfunction __construct($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);