Database migrations - Django Web Development Tutorial

Welcome to Part 8 of our Django web development with Python tutorial.

Remember how when you create a new app, the first thing you need to do is install it? Whenever you define new models, you want to migrate. If you are familiar with older versions of Django, the old syncdb command is deprecated. Nowadays, first you will do

python manage.py makemigrations

Output:

Migrations for 'blog':
    0001_initial.py
        - Create model Post

This makemigrations command tells Django that you've made some model changes, and you want to save them as a migration. Migrations are used any time you want Django to recognize changes to the models and database schema. Adding data to an existing database table, for example, is not something that needs a migration, changing that table's structure (by changing the model), would require a migration. With the above command, you will now have a blog/migrations directory, containing the proposed migration. You can also tell Django you want to make migrations for only a specific app, like:

python manage.py makemigrations blog

Once you've made migrations, nothing has actually happened yet. You can run a migrate, but there is one more check you can make:

python manage.py sqlmigrate blog 0001

This will output the proposed SQL that will be run for you by Django when you migrate. It is a good idea to just read it over. For example, mine is:

If all looks good, then you will do python manage.py migrate. This will actually perform the migrations. If this is your first time doing this, you should see quite a bit has been migrated:

Most of this migration is actually for the default Django code in our application, much of which corresponds to the admin page that we have yet to see, but some of that is indeed our blog model. Behind the scenes, Django has actually made our SQL table for us.

Okay, let's do python manage.py runserver and see if we can load //127.0.0.1:8000/blog/. That should load, but there's nothing here. No surprise, we haven't written anything in our blog! That's what we're going to cover in the next tutorial.

Download the entire site's code for this tutorial here: Part 8

The next tutorial: Admin control panel - Django Web Development Tutorial