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 $course; public function __construct($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);