Now that you’ve verified the connection is working, it’s time to create a Django app — a bundle of Django code, including models and views, that lives together in a single Python package and represents a full Django application.
It’s worth explaining the terminology here, because this tends to trip up beginners. We’d already created a project, in Chapter 2, so what’s the difference between a project and an app? The difference is that of configuration vs. code:
- A project is an instance of a certain set of Django apps, plus the configuration for those apps.Technically, the only requirement of a project is that it supplies a settings file, which defines the database connection information, the list of installed apps, the TEMPLATE_DIRS, and so forth.
- An app is a portable set of Django functionality, usually including models and views, that lives together in a single Python package.For example, Django comes with a number of apps, such as a commenting system and an automatic admin interface. A key thing to note about these apps is that they’re portable and reusable across multiple projects.
There are very few hard-and-fast rules about how you fit your Django code into this scheme; it’s flexible. If you’re building a simple Web site, you may use only a single app. If you’re building a complex Web site with several unrelated pieces such as an e-commerce system and a message board, you’ll probably want to split those into separate apps so that you’ll be able to reuse them individually in the future.
Indeed, you don’t necessarily need to create apps at all, as evidenced by the example view functions we’ve created so far in this book. In those cases, we simply created a file called views.py, filled it with view functions, and pointed our URLconf at those functions. No “apps” were needed. However, there’s one requirement regarding the app convention: if you’re using Django’s database layer (models), you must create a Django app. Models must live within apps. Thus, in order to start writing our models, we’ll need to create a new app. Within the mysite project directory you created in Chapter 2, type this command to create a new app named books:
python manage.py startapp books
This command does not produce any output, but it does create a books directory within the mysite directory. Let’s look at the contents of that directory (showing the project folder tree so you can see where the app should be located):
\mysite_project
\books
\migrations
__init__.py
admin.py
apps.py
models.py
tests.py
views.py
\mysite
\templates
manage.py
These files will contain the models and views for this app. Have a look at models.py and views.py in your favorite text editor. Both files are empty, except for comments and an import in models.py. This is the blank slate for your Django app.
