Api/plugins for open source libraries?

Question

whenever i use a open source library eg. Doctrine i always ending up coding a class (so called Facade) to use the Doctrine library.

so next time i want to create a user i just type:

 $fields = array('name' => 'peter', 'email' => '[email protected]');
 Doctrine_Facade::create_entity($entity, $fields);

then it creates an entity with the provided information.

so i guess, all coders will create their own "Facade".

i wonder how usual it is with open source Facades to download and interact with the open source libraries? is this rare cause i haven't seen any of these. in some frameworks i have seen them called plugins, eg. plugins for twitter api or facebook api.

so whenever you download a library, should you search for plugins/facades on the net, or is it better to just try coding your own? i just thought it would be great for everyone not to reinvent the wheel.

thanks.

Answer 1

The aim of a Facade is to (quoting)

• Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.
• Wrap a complicated subsystem with a simpler interface.

While the above can be said to apply to your example, it feels much more like an AbstractFactory to me. You might want to rename it to EntityFactory without the Doctrine part, because the fact that it uses Doctrine internally is an implementation detail. For the public facing API of the Factory, it doesn't matter. Maybe you want to change from Doctrine to Propel at a later time and then you just have to change the code inside the class, but not the API.

You might also be interested in the Gateway pattern.

But to answer your question whether this is a common approach: yes, I think so. Abstraction makes code easier to understand and easier to maintain. But since the API of the facade/gateway - whatever applies - is usually determined by what the application does, it rarely can be reused, so I doubt you will find readymade facades/gateways on the web.

Answer 2

Let us say it is not just about Factories, let us say, you really often write Facades for libraries you use. What is the point? Why are you doing it? The point is, that you use the library in a specific way. If the Facade you write was universal and everybody tended to write something like that, the Facade would be surely part of the library. So the reason why it is not and why you want to write it is, that you use it in a very specific way, which is specific to you application of the library. So you transition from the abstraction of the library to the abstraction of your application. This can remove much of the complexity of the library from your application, but it also restricts the way in which you use the library. So, if you understood my point, you might be convinced, that there is no point in releasing each Facade for certain way in which the library can be used. However, sometimes, when we talk about a big influential library, which is combined with some other libraries and together comprise abstraction, which can be widely used, it may happend that new library will be created.