Question

Magento is a newish (past 5 years) PHP based Ecommerce system with an architecture that’s similar to the Java Spring framework (or so I’ve been told)

One of the features of the Framework is certain classes are not directly instantiated. Rather than do something like

$model = new Mage_Foo_Model_Name();

you pass an identifier into a static method on a global application object

$model = Mage::getModel('foo/name');

and this instantiates the class for you.

One of the wins with this approach is getModel checks a global configuration system for the foo/name identifier, and instantiates the class name it finds in the configuration system. This allows you to change the behavior of a Model system wide with a single configuration change.

Is there a formal, Gang of Four or otherwise, name that describes this system/design pattern? The instantiation itself looks like a classic Factory pattern, but I’m specifically interested in the whole “override a class in the system via configuration” aspect. Is there a name/concept that covers this, or is it contained within the worldview of a Factory?

Answer 1

This looks like the Factory design pattern.

Quoting the wikipedia entry for Factory method pattern (emphasis mine) :

it deals with the problem of creating
objects (products) without specifying
the exact class of object that will be
created.
The factory method design
pattern handles this problem by
defining a separate method for
creating the objects, which subclasses
can then override to specify the
derived type of product that will be
created.

And :

Outside the scope of design patterns,
the term factory method can also refer
to a method of a factory whose main
purpose is creation of objects.

A couple of other interesting links :

• Factory (software concept)
• Factory pattern