Adding Flask-Migrate to an Existing Flask-SQLAlchemy Project

Flask-Migrate is a Flask extension that helps you manage database migrations in a Flask-SQLAlchemy project. This tutorial will guide you through the process of adding Flask-Migrate to an existing Flask-SQLAlchemy project.

Step 1: Install Flask-Migrate
The first step is to install Flask-Migrate. You can do this using pip:

pip install Flask-Migrate

Step 2: Create a Migration Repository
After installing Flask-Migrate, you need to create a migration repository. To do this, run the following command in your project directory:

flask db init

This command will create a ‘migrations’ directory in your project with a ‘versions’ subdirectory where all the migration scripts will be stored.

Step 3: Configure Flask-Migrate
Next, you need to configure Flask-Migrate in your Flask application. Add the following lines of code to your Flask application:

from flask_migrate import Migrate
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///mydatabase.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False

db = SQLAlchemy(app)
migrate = Migrate(app, db)

In this code snippet, we are initializing Flask-Migrate with our Flask application and SQLAlchemy database.

Step 4: Create an Initial Migration
Now that Flask-Migrate is configured in your Flask application, you need to create an initial migration that represents the current state of your database. To do this, run the following command:

flask db migrate -m "initial migration"

This command will generate a migration script in the ‘versions’ directory with the changes required to create your database tables.

Step 5: Apply the Migration
After creating the initial migration, you need to apply it to your database. To do this, run the following command:

flask db upgrade

This command will execute the migration script and apply the changes to your database.

Step 6: Create and Apply Subsequent Migrations
Whenever you make changes to your database schema, you need to create a new migration and apply it to your database. To create a new migration, run the following command:

flask db migrate -m "description of changes"

This will generate a new migration script in the ‘versions’ directory with the changes you made to your database schema. To apply the new migration, run the following command:

flask db upgrade

This will execute the new migration script and apply the changes to your database.

By following these steps, you can easily add Flask-Migrate to an existing Flask-SQLAlchemy project and manage database migrations effectively. Happy coding!