A brief analysis of the design of Collection class in PHP

A brief analysis of the design of Collection class in PHP_PHP Tutorial

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Release： 2016-07-21 15:04:02

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I have been developing with .net for many years. I recently came into contact with php and found that php is also very fun. However, I found that there is no Collection class in it, only arrays, and arrays are very powerful. Here I use an array to wrap it into a Collection. The code is as follows:

Copy code The code is as follows:

class Collection{
private $_members=array();

public function addItem($obj,$key=null)
{
if($key)
if(isset ($this->_members[$key]))
                                                                                                                                                                                                    🎜>              $this->_members[$key]=$obj;
                                                                  gt;_members[]=$obj;
}
}

public function removeItem($key)
{
if(isset($this->_members[$key]))
{
unset( $this->_members[$key]);

public function getItem($key)
{
if(isset($this->_members[$key]))
{
return $this->_members[$key] ];
}
else
{
throw new exception("Invalid Key "$key"!"); Keys( )
                                                                                                                                                                                                                                                                      ;     );
}

public function exists($key)
{
return (isset($this->_members[$key]));
}
}

Now let’s test whether this collection is easy to use.
We first create a collection element class Course:

Copy the code

The code is as follows:

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：

复制代码代码如下:

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：

复制代码代码如下:

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);