Django: Best practices for database design

Question

I'm starting a project and i've decided to use Django.

My question is regarding to the creation of the database. I've read the tutorial and some books and those always start creating the models, and then synchronizing the DataBase. I've to say, that's a little weird for me. I've always started with the DB, defining the schema, and after that creating my DB Abstractions (models, entities, etc).

I've check some external-pluggable apps and those use that "model first" practice too.

I can see some advantages for the "model-first" approach, like portability, re-deployment, etc.

But i also see some disadvantages: how to create indexes, the kind of index, triggers, views, SPs, etc.

So, How do you start a real life project?

Answer 1

Triggers, views, and stored procedures aren't really a part of the Django world. It can be made to use them, but it's painful and unnecessary. Django's developers take the view that business logic belongs in Python, not in your database.

As for indexes, you can create them along with your models (with things like db_index and unique_together, or you can add them later via database migrations using something like South.

Answer 2

Mostly we don't write SQL (e.g. create index, create tables, etc...) for our models, and instead rely on Django to generate it for us.

It is absolutely okay to start with designing your app from the model layer, as you can rely on Django to generate the correct database sql needed for you.

However, Django does provide various functions for you to replicate these database functions:

• triggers: Django code or MySQL triggers
• indexes: can be specified with db_index=True
• unique constraints: unique = True or unique_togther = (('field1', field2'),) for composite unique constraint.

The advantage with using Django instead of writing sql is that you abstract yourself away from the particular database you are using. In other words, you could be on SQLite one day and switch to PostgresQL or MySQL the next and the change would be relatively painless.

Example:

When you run this:

python manage.py syncdb 

Django automatically creates the tables, indexes, triggers, etc, it needs to support the models you've created. If you are not comfortable with django creating your database for you, you can always use:

python manage.py sqlall 

This will print out the SQL statements that Django would need to have in order for its models to function properly. There are other sql commands for you to use:

see: https://docs.djangoproject.com/en/1.3/ref/django-admin/#sql-appname-appname