How to use Flask-Migrate for database migration

How to use Flask-Migrate for database migration

Introduction:
When developing web applications, database migration is a very important link. When our applications require structural changes to the database, database migration can help us manage these changes conveniently and ensure the security of the data. In the Flask framework, we can use Flask-Migrate to perform database migration. This article will introduce how to use Flask-Migrate to perform database migration and give some code examples.

1. Install Flask-Migrate
Before we begin, we need to install Flask-Migrate.

Execute the following command in the terminal:

pip install Flask-Migrate

2. Configure Flask-Migrate
In our Flask application, we need to make some configurations to enable the function of Flask-Migrate. First, create a command line script in our Flask application, such as manage.py. In this script, we need to do some initial configuration.

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = '数据库连接字符串'

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

In the above code, we first create a Flask application object app, and then configure the database connection string. Next, we created a SQLAlchemy database instance db and a Flask-Migrate instance migrate.

3. Create a migration script
After configuring Flask-Migrate, we can use the following command to generate a database migration script:

python manage.py db init

This will be created in our application directory A directory named migrations is used to store database migration scripts.

Next, we need to use the following command to generate a new migration script:

python manage.py db migrate -m "迁移描述"

In the above command, we can add migration description information through the -m parameter , describing the changes made by this migration. This will generate a new migration script in the migrations/versions directory.

4. Apply migration script
After generating the migration script, we can use the following command to apply the migration script, that is, to apply the structural changes of the database to the database:

python manage.py db upgrade

The above command will update the database according to the migration script in the migrations/versions directory.

5. Undo the migration
If we need to undo the most recent migration operation, we can use the following command:

python manage.py db downgrade

The above command will undo the most recent migration operation and restore it to the previous version .

6. Other commonly used commands
In addition to the above commands, Flask-Migrate also provides some other commonly used commands for managing the database migration process. For example:

• python manage.py db history: View database migration history.
• python manage.py db current: View the current database version.
• python manage.py db show: Display detailed information of the current database.

7. Summary
This article briefly introduces the process of how to use Flask-Migrate for database migration. First, we need to install Flask-Migrate and make the necessary configurations. We can then use a series of commands to generate, apply, and undo the database migration script. Finally, we also introduced some other commonly used commands to facilitate us in managing the database migration process.

Flask-Migrate is a very powerful and convenient tool that can help us manage database migration easily. I hope this article can help readers to better use the Flask framework for database migration.

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