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Flask-Migrate: Using Python to migrate databases
With the continuous development of web development, the importance of databases has become increasingly prominent. During the development process, we need to modify and migrate data. However, if you modify it directly on the database, it may bring unpredictable risks. At this time, Flask-Migrate came into being. In this article, we will focus on the use of Flask-Migrate and how to migrate databases through Python.
Introduction to Flask-Migrate
Flask-Migrate is a database migration framework used in conjunction with the Flask framework. It provides an easy way to version and migrate databases. It allows us to make modifications to the database without deleting any data, which means we don't need to worry about data loss or incompatibility. At the same time, Flask-Migrate also supports a variety of databases, including SQLite, MySQL and PostgreSQL.
Installation of Flask-Migrate
Before we start using Flask-Migrate, we need to install it first. Flask-Migrate can be easily installed using the pip command:
pip install Flask-Migrate
After the installation is completed, we can start using Flask-Migrate.
Usage of Flask-Migrate
Before using Flask-Migrate, we need to initialize the Flask application. Here, we use a simple Flask program as an example:
from flask import Flask from flask_sqlalchemy import SQLAlchemy app = Flask(__name__) app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db' db = SQLAlchemy(app) class User(db.Model): id = db.Column(db.Integer, primary_key=True) username = db.Column(db.String(80), unique=True) email = db.Column(db.String(120), unique=True) def __init__(self, username, email): self.username = username self.email = email def __repr__(self): return '<User %r>' % self.username
The above code uses the Flask_sqlalchemy extension to configure the database connection. It defines a User model and related properties.
Initialize the database
Before performing database migration, we need to create the database first. In Flask, you can use the db.create_all()
function to create all defined models:
from app import db db.create_all()
At this time, a SQLite database named test.db will be automatically created in the database, and The table has been created according to the defined model properties.
Migrate database
Based on the above initialization of the database, we can migrate the database. Performing database migration requires two steps: generating the migration script and applying the migration script.
Generate migration script
The command to generate migration script is:
flask db migrate
After executing this command, Flask-Migrate will automatically detect the structure of the model definition and database, and will detect Generate a migration script based on the differences. At this point, we can view the script in the migrations/versions
folder in the project folder. This script is a Python module that contains the differences between the current model and the database.
Apply migration script
After generating the migration script, you need to apply it to the database. This process is called migration.
flask db upgrade
After executing this command, Flask-Migrate will upgrade the table structure based on the generated migration script. At this point, we can view the changed table structure in the database.
Summary
In this article, we introduced the basic usage of Flask-Migrate. With Flask-Migrate, we can easily manage the structure of database tables. Its advantage is that it can conveniently maintain data security and consistency, and can be easily versioned. In actual projects, if we need to modify and manage the database, we can choose to use the Flask-Migrate tool.
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