Flask-Migrate
Tags: flask
Published: 2023-11-21 22:10:00

Flask-Migrate is an important extension in the Flask ecosystem. The extension was created to handle SQLAlchemy database migrations for Flask applications using Alembic. Using Flask-Migrate makes adding tables/ columns, modifying existing columns, and deleting outdated columns a simple and easy process. 

## Installation

You can install Flask-Migrate with pip by typing this command into the terminal:

`pip install Flask-Migrate`

## Migration Workflow

When developers make alterations to the database schema, Flask-Migrate automates the generation of migration scripts. These scripts act as a representation of the differences between the current state of the database and the desired changes. 

In order for all of the following commands to work, the application script must be set in the FLASK_APP environment variable. The migration workflow typically starts with running the `flask db init` command. This command will add a migrations folder to your application. The contents of this folder must be created in order to version control along with your other source files. 

After running this command, you can then create an initial migration by running `flask db migrate -m "Initial migration"` (the message is optional but can be helpful for signifying what changes you made to the table). This command generates the migration script. Since Alembic is not always able to detect every change you make to your models (it currently is unable to detect table name changes, column name changes, or anonymously named constraints), it is important to review and edit the migration script as needed. 

Finally, you can run the `flask db upgrade` command, which applies the generated migration script to the database, ensuring that the changes are executed effectively. Each time the database models are altered, repeat the migrate and upgrade commands. The migrate command will create new scripts based on the alterations, and the upgrade command will execute them. 

## Downgrading

One advantage of using Flask-Migrate is its ability to handle rollback operations. In situations where a migration script needs to be reverted to a previous migration state, the `flask db downgrade` command can efficiently rolls back the changes. Running this command restores the previous state of the database. You can also specify a revision number at the end of the command to downgrade to a version that is more than one downgrade away from the current database state. 

## Facilitating Collaboration

Another benefit of using Flask-Migrate is its ability to facilitate collaboration among team members working on the same project. With the unique version numbers for each new migration, along with the ability to write a migration message in order to explicitly explain which changes were made, developers can easily track and manage changes made by different team members. This helps maintain consistency and ensures that everyone can work with the same database schema. 

Altogether, Flask-Migrate significantly simplifies the management of database schema migrations in Flask applications. Below is a link to the documentation page for the extension. {% embed https://flask-migrate.readthedocs.io/en/latest/ %}