Manage the database
The Django ORM goes beyond allowing you to interact with data. You can also use it to create and update the database itself through a process known as migrations.
Migrations
A migration is a collection of updates to be performed on a database's schema. A database schema is the definition of the database itself, including all tables and columns, and relationships between those tables.
When we created our models and defined the fields, we also defined the tables, columns, and relationships between those tables. We created our schema definition by creating our models!
Migrations are used to create and update the database as our models change. As you likely know, software is constantly changing. How we define our models today might be different from how we define them tomorrow. Migrations abstract the process of updating the database away from us. We can then make changes to our models and use Django to perform the necessary changes to the database.
Make a migration
To create a migration, you use the makemigrations command in manage.py. The makemigrations command uses the current list of migrations to get a starting point, and then uses the current state of your models to determine the delta (the changes that need to be made). It then generates the necessary code to update the database. After makemigrations runs, it displays the name of the migration.
python manage.py makemigrations
Display the SQL for the migration
Any operations that happen inside a relational database require Structured Query Language (SQL). Django's migrations generate the appropriate SQL when they're run. Although you can use the migration tools to update your database directly, some environments might have database administrators who will manage the process for you.
To build the appropriate SQL statements, you can use sqlmigrate.
python manage.py sqlmigrate <app_label> <migration_name>
Note
The app_label part is the name of your app, typically the name of the folder that contains your app. The migration_name part is the name of the migration. You can also see the Python code for any app's migrations in its migrations folder.
Display the list of migrations
If you want to see all migrations, you can use showmigrations.
python manage.py showmigrations
Perform a migration
The migrate command runs a specific migration or all migrations on the database configured in settings.py in the root of your project folder.
If you open settings.py, you'll see a DATABASES section at the bottom. This section includes a default option, which on a new project is configured to use SQLite. You can configure different database connection strings in this section as needed.
python manage.py migrate <app_label> <migration_name>
Note
The app_label and migration_name parts are optional. If you don't provide either, all migrations will run. You'll use this command often during development.