The next step in the process is to create a database migration repository. This is a directory where all the migration scripts are going to be stored. The migration repository should be considered part of your source code, and should be added to your source control.
- With Flask-Migrate and Alembic, it is possible to downgrade to an older revision of your database.
- Once finalized, the migration script also needs to be added to version control.
- In case, you haven’t applied any migration it will return nothing.
- Fields are assigned a type using Python type hints, wrapped with SQLAlchemy’s so.Mapped generic type.
Each time the source code changes or new database migrations are created, a new container can be deployed that automatically applies database changes and runs our application. Now I will show how Flask-Migrate flask developer can be used in Flask applications. We will create a simple application with a database table for posts. After modifying your database model, generate a migration script based on this modification.
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The function can modify the configuration object, or replace it with a different one. Alembic also tracks each of these migrations over time, so that you can easily go to a past version of the database. This is useful if bugs are introduced or the feature requirements change. As you https://remotemode.net/ work on your application, particularly over a long time, it is unavoidable that you will want to add columns to your models, or even add new models entirely. This is why it’s important to never rename the migration files or change the revision identifiers at the top of those files.
Flask is a lightweight Python web framework that provides valuable tools and features for creating web applications in the Python Language. SQLAlchemy is an SQL toolkit offering efficient and high-performing relational database access. It provides ways to interact with several database engines, such as SQLite, MySQL, and PostgreSQL. It also gives you an Object Relational Mapper (ORM), which allows you to make queries and handle data using simple Python objects and methods. Note that the application script must be set in the FLASK_APP environment variable for all the above commands to work, as required by the flask command.
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You should review it and edit it to be accurate, as Alembic cannot detect all changes that you make to your models. In particular it does not detect indexes, so those need to be added manually to the script. Note how in the first two examples above the relationship between users and posts is used. Recall that the User model has a posts relationship attribute that was configured with the WriteOnlyMapped generic type. This is a special type of relationship that adds a select() method that returns a database query for the related items.
