Impressions on Django (I)

During the last months, I've been involved in a project on (text) information retrieval. The project required to develop a web interface over a python core and we chose Django as framework. Other option was using plain mod_python as we did for EfficiencyGuardian. But some time ago, in the context of the SIMAC project, Xavier Oliver, who was the responsible of implementing BOCA, CLAM Annotator's collaborative back-end, used Django and he was very enthusiastic on how rapid he had all the web working. So I wanted to give it a try for our current work. Here I am posting my first impressions as newbie django user. What Django has to offer?

Database abstraction

The most important part of Django is a persistent object model which maps python objects into database entities giving you a nice abstraction on the database layer. By defining such model classes, you get an object oriented programming interface to query and change related database tables, and even navigating and joining through relations as they were regular connected objects.

I normally dislike too transparent interfaces when they deal with efficiency sensible things such as database access. But Django states very clearly when and how such access is done allowing you to control it but using a high level object oriented idiom.

Administration interface

You can enable an existing administration module for your site. That is a web interface to create, edit and remove your model objects. You can control the way they are edited by adding extra properties to the model classes attributes.

Attributes have more types than real SQL types. Fields can be, for example, URL's, emails, telephone numbers or zip codes, and Django gives you for free custom validation and custom administration interfaces for them.

The administration interface also considers table relations providing, for instance, web interfaces for choosing related objects by foreign key and buttons to add a new related objects.

Application logic

Often, as in our case, the administration interface is pretty close to what the final application will be. But direct manipulation of a model is not enough for most web applications. Normally you need some additional application logic: Which functionalities are presented to the user, and which is the user dialog with the system to perform such functionalities.

Three elements are combined to build up such application logic in Django: URL mappings, views and page templates. URL mappings map regular expressions of requesting URL into calls to python functions. Such pỳthon functions are the views which perform the needed actions on the system and construct an output web page. Views usually inject python data into an HTML skeleton, the page template, to generate the response web page.

Django provides some convenience views to create, update, delete and listing model objects, also supporting common features such as pagination, date based browsing, validation and destructive action confirmation.

The next entry

Here i explained the basics of Django execution model. On the next entry i'll write some impressions on Django as development environment compared to other environments i used for web development such as Zope, mod_python and vanilla PHP.