Flask-Migrate is an extension that handles SQLAlchemy database migrations for Flask applications using Alembic. The database operations are provided as command line arguments for Flask-Script.
Install Flask-Migrate with pip:
pip install Flask-Migrate
This is an example application that handles database migrations through Flask-Migrate:
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask_script import Manager
from flask_migrate import Migrate, MigrateCommand
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///app.db'
db = SQLAlchemy(app)
migrate = Migrate(app, db)
manager = Manager(app)
manager.add_command('db', MigrateCommand)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(128))
if __name__ == '__main__':
manager.run()With the above application you can create the database or enable migrations if the database already exists with the following command:
$ python app.py db init
This will add a migrations folder to your application. The contents of this folder need to be added to version control along with your other source files.
You can then generate an initial migration:
$ python app.py db migrate
The migration script needs to be reviewed and edited, as Alembic currently does not detect every change you make to your models. In particular, Alembic is currently unable to detect indexes. Once finalized, the migration script also needs to be added to version control.
Then you can apply the migration to the database:
$ python app.py db upgrade
Then each time the database models change repeat the migrate and upgrade commands.
To sync the database in another system just refresh the migrations folder from source control and run the upgrade command.
To see all the commands that are available run this command:
$ python app.py db --help