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This article shows you how to do database migration in Flask. It is concise and easy to understand. It will definitely make your eyes shine. I hope you can gain something from the detailed introduction of this article.

# pip install flask-migrate

#coding=utf-8

from flask import Flask

from flask_sqlalchemy import SQLAlchemy

from flask_migrate import Migrate,MigrateCommand

from flask_script import Shell,Manager

app = Flask(name)

manager = Manager(app)

app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://root:mysql@127.0.0.1:3306/Flask_test'

app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN'] = True

app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True

db = SQLAlchemy(app)

#The first argument is an instance of Flask, the second argument is an instance of Sqlalchemy database

migrate = Migrate(app,db)

#manager is an instance of Flask-Script, which adds a db command to Flask-Script

manager.add_command('db',MigrateCommand)

#Define the Role of the model

class Role(db.Model):

#Define table name

__tablename__ = 'roles'

#Define column objects

id = db.Column(db.Integer, primary_key=True)

name = db.Column(db.String(64), unique=True)

user = db.relationship('User', backref='role')

#repr() method displays a readable string,

def __repr__(self):

return 'Role:'.format(self.name)

#Define user

class User(db.Model):

__talbe__ = 'users'

id = db.Column(db.Integer, primary_key=True)

username = db.Column(db.String(64), unique=True, index=True)

#Set foreign key

role_id = db.Column(db.Integer, db.ForeignKey('roles.id'))

def __repr__(self):

return 'User:'.format(self.username)

if __name__ == '__main__':

manager.run()

```

#The following are the operations performed at the terminal

Create Migration Repository #This command creates the migrations folder where all migration files will be placed. python database.py db init Create migration script

There are two functions to automatically create migration scripts

upgrade(): The function applies changes made during migration to the database.

downgrade(): The function removes the change.

An automatically created migration script generates the contents of the upgrade() and downgrade() functions based on differences between the model definition and the current state of the database.

The comparison may not be completely correct, and some details may be missed, which needs to be checked.

python database.py db migrate -m 'initial migration' update database python database.py db upgrade return previous version

You can find the version number by following the history command and pass it to the downgrade command:

python app.py db history Output format: -> version number (head), initial migration

Rollback to a specified version

python app.py db downgrade version number actual operation order:

1. Python file db init

2. python file db migrate -m"Version name (comments)"

3. Python file db upgrade and then observe the table structure

4. Modify the model according to requirements

5. python file db migrate -m"New version name (comments)"

6. Python file db upgrade and then observe the table structure

7. If the version is returned, use the python file db history to view the version number

8. python file db downgrade(upgrade) version number

That's how database migration works in Flask. Have you learned anything or skills? If you want to learn more skills or enrich your knowledge reserves, please pay attention to the industry information channel.

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