Monday, July 06, 2009

Becoming a Doctrine 2 committer

In the last weeks I started to contribute with code to the Doctrine project. Doctrine is an Orm and database abstraction layer for php: it is the default orm for Symfony but it's not coupled to it and I integrated it successfully with Zend Framework. It is a good tool for abstracting the database layer and manage the persistence of the Model part of a MVC paradigm, which to me Zf does not very well with its Zend_Db component.

After opening tickets and upload patches for Doctrine 1.x for some months, I took a glimpse of the potentiality of the 2.x branch (that currently is not even in alpha). The code is in the trunk of the Doctrine repository and borrows concepts heavily from Hibernate:
While Doctrine Query Language, based on Hql, was already present in the currently stable 1.x branch, the new Doctrine infrastructure is based on the Unit Of Work pattern instead of the old Active Record one.
The Active Record pattern is very famous and is used for example in Rails. It is the most simple solution of object relational mapping, which defines a class for every table of the database. A row is represented by an object of that class, that is subclassing Doctrine_Record/ActiveRecord depending on the framework and language you are using.
The Unit Of Work pattern does not substitute by itself the Active Record one, but it's part of the solution of refusing to have the domain objects depending on the infrastructure, in this case the mapping classes. This is very clean from a design and testing point of view as the most complex logic of an application resides in the domain classes (the User and Phonenumber ones for instance), and Doctrine 2 let the developer concentrate on writing and testing these models without (almost) taking into account where they will be persisted; how to map these classes is specified in annotations or via other metadata.
If you have written a bit of code you will probably find very interesting these solution, that is already used in Hibernate for the joy of Java programmers.

Said that, I really want to help the project as I dream of doing Domain Driven Design in php and persistence ignorance is a key point of DDD. So I asked how to start contribution to the project and the last week I've written eight test case class for phpunit plus the example model classes that they use. I was helped by Roman Borschel, the lead developer for the 2.x branch, that teached me how to use annotations properly and fixed my faults in the model classes. Keep in mind that contributing to an open source project you use or will use is a win-win situation because it helps the project going forward and obtain feedback, while it helps you to learn to use the tool well. And I will certainly use Doctrine 2 because I think it along with Zend Framework will kick Rails in the ass.

This monday, I have succesfully closed ticket #2276 and I look forward to learn more and go further. If you are a php developer, come to #doctrine-dev on the irc server, or stay tuned to try the alpha releases of Doctrine 2 that will come in the future. Having a real domain model, free of dependencies versus concrete orms, is a dream of the php world that will be realized.

1 comment:

Fedyashev Nikita said...

Good job!

IMO, Doctrine2 is a big step for writing a better PHP code.

I'm waiting for more stable version of Doctrine and willing to start use it as soon as possible.

Unfortunately there isn't lots of information about persistence-ignorant domain in PHP environment. But thanks for your posts describing this topic :)