Question

Well,

I have a problem (ok, no real problem, but I wanna try out something new) with creating objects. Actually I have some orders, which contains a list of orderitems.

These orderitems are used and so spreaded in the whole application, and I need a way to create them. The main problem is, I want to be able to create these objects in many different ways.

Actually I do this in the class constructor and check if the argument which is given.
(I’m using php, so there is no overloading support from the language as you surely know :))

A simple and quick Example

class foo {
    protected $_data=null;
    public function __contruct($bar){
        if (is_array($bar)){
            $this->_data=$bar;
        }
        else {
            $dataFromDb=getDataFromDatabase
            $this->_data=$dataFromDb;
        }
    }
}

Anyway, if I want to create my object by giving another type of parameter, lets say a xml-document encapsulated in a string I need to put all this stuff in my constructor.
If the process for creating an object is more complicated, I eventually need to create a seperate method for each type, I want to initiate. But this method is only called when this special type is created. (I think you got the problem :))

Another problem comes to mind, if I need more parameters in the constructor to create a concrete object, I have modify all my code, cause the contructor changed. (Ok, I can give him more and more parameters and work with default values, but that is not what I really want).

So my Question is, which pattern fits this problem to solve my creation of a concrete object. I thought about creating a factory for each way I want to create the concrete object. But I’m not sure if this is a common solution to solve such a problem.

Answer 1

IF its only the signature of the constructor changing i would do it like so (a la the Zend Framework universal constructor):

class foo {
  // params

  public function __construct($options = null)
  {

    if(null !== $options)
    {
       $this->setOptions($options);
    }
  }

  public function setOptions(array $options){

    foreach ($options as $name => $value){
      $method = 'set' . $name;
      if(method_exists($this, $method)
      {
         $this->$method($value);
      }
   }

   return $this;
  }
}

And this essntially means all your constructor parameters are array elements with named keys, and anything you want used in this array during initialization you create a setter for and then its automatically called. The down side is the lack of effective hinting in IDEs.

On the otherhand if you want to have specific constructors then i might go with a factory but still use much the same approach:

class foo {

  public static function create($class, $options)
  {
     if(class_exists($class))
     {
        $obj = new $class($options);
     }
  }
}

Of course you could alternatively use PHP’s reflection to determine how to call the constructor instead of just injecting an arbitrary array argument.