Projects and Applications

In theory, as long as Python can find everything, you can organise your own web application code however you want; however, we might as well follow the default Django way until we have a good reason not to. A Django website is normally organised into a 'project' which contains 'applications'.

A project has a database, most small to medium websites will only need one database so therefore will only need one project. Of course, the web server (i.e. Apache) can host many Django projects under a single domain name, but for now we will assume that we have just one project for this website.

So under the project we have applications. These provide the dynamic and interactive functionality of the web site. These are the fun bits! We might have, for example, stories, comments, quizzes, rss feeds, or whatever else you can think of. Each of these things can be a separate application.

Starting a project

So in the last post we got a database ready and installed Django to the system. Now we want to create a project:

django-admin.py startproject mysite

You may need to leave out the .py depending on your distribution and how you got Django. The command that works is the correct one!

django-admin startproject mysite

This command creates a directory with four files inside. Two are fluff that we do not edit:

__init__.py is just a stub that lets the Python interpreter view the directory as a Python package.

manage.py is a tool that provides some friendly command line abstractions of Django features.

The remaining two files are the interesting ones.

urls.py

urls.py contains your URL mappings, i.e. it maps the URLs to the applications. This is also sometimes called 'request dispatching'. This function is called routes in Pylons and Ruby on Rails.

What does this mean? Well a 1990s-style static website will just be 'piles of files'. When the request comes in, the webserver will return a file, end of story. No logic is involved.

URL mapping is what distinguishes a 21st Century dynamic web application from that. When the request comes in, the relevant code will run and then a webpage will be generated and returned with a pretty URL that looks however you want.

So for example, let's imagine a Django powered blog. In this case, a user requests the URL http://some.where/feeds/ which is then handled by the feeds application which generates an RSS feed of the latest posts.

Your urls.py is rather empty at the moment, but in a completed Django website, urls.py may have a number of lines that look something like this:

(r'^feeds/$', 'mysite.feeds'),

The first half is a regular expression, the second part is the application that is handling the request. So if the URL matches the first part, then the application on the right is in charge. The urls.py directives will be more complicated in a real-life examples of course.

If you are confused by the first part, don't worry too much at this point. For the sake of completeness, r means that the string should be interpreted by Python as a raw string (i.e. don't escape n and so on). ^ and $ are Python regular expression syntax for the start and end of the string.

settings.py

The file settings.py, as you might have guessed, is your project's settings, such as the database settings, what applications you have installed, what your time zone is, where your static files are and so on. It is just a simple config file. It a basic python file not .ini format, so remember the quote marks around strings or you will get errors. For example:

TIME_ZONE = 'Europe/London'

Add your database information to settings.py now using the four pieces of information that you recorded in the last post. It should look something like this:

DATABASE_ENGINE = 'mysql'

DATABASE_NAME = 'djtest'

DATABASE_USER = 'djangouser'

DATABASE_PASSWORD = 'password'

Now we will create the initial database tables, the following command syncs the database to match the current state of our project.

python manage.py syncdb

Since this is the first time we have run it in this project, it will give you the choice of creating a superuser account. Accept it and take note of what you have entered, you will need it later.

Now we are ready to create applications. We will leave that for the next post. In the meantime, you might want to test your project by running the test server:

python manage.py runserver 8080

In your web-browser, enter the URL http://127.0.0.1:8080/

With a bit of luck you will get the Django welcome screen telling you that Django works.

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