How to migrate databases in the flask framework

Flask How to migrate databases in the framework

Flask Data migration in the framework requires installation Flask-Migrate plug-in unit
Installation command ：pip install flask-migrate
Definition ORM Model

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

app = Flask(__name__)

#  Configuration variables of the database 
HOSTNAME = '127.0.0.1'
PORT = '3306'
DATABASE = 'zzh_flask'
USERNAME = 'root'
PASSWORD = 'root'
DB_URI = 'mysql+pymysql://{}:{}@{}:{}/{}?charset=utf8'.format(USERNAME, PASSWORD, HOSTNAME, PORT, DATABASE)

#  The defined database connection string DB_URI, adopt `SQLALCHEMY_DATABASE_URI` This key Name configuration to `app.config` in .
app.config['SQLALCHEMY_DATABASE_URI'] = DB_URI
#  Set whether to track every database modification 
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True
#  Use `flask_sqlalchemy.SQLAlchemy` This class defines an object , And will `app` Put it in .
db = SQLAlchemy(app)

#  Create a migrate object 
migrate = Migrate(app, db)


#  Definition ORM Model 
class User(db.Model):
    __talblename__ = 'user'
    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    username = db.Column(db.String(200), nullable=False)


class Article(db.Model):
    __tablename__ = 'article'
    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    title = db.Column(db.String(200), nullable=False)
    content = db.Column(db.Text, nullable=False)

    #  Foreign keys 
    # 1. The data type of the foreign key must depend on , The type of the field being referenced 
    # 2.db.ForeignKey(" Table name . Field name ")
    # 3. Foreign keys belong to the database level , It's not recommended to go directly to ORM Use in 
    # db.ForeignKey Declare that this field is a foreign key 
    author_id = db.Column(db.Integer, db.ForeignKey("user.id"))

    # relationship
    # 1. The first parameter is the name of the model , Must be consistent with the name of the model 
    # 2.backref(back reference): Represents a reverse reference ,"articles" Field name when accessing me on behalf of the other party , The premise is that a foreign key has been associated in the front 
    #  The function here is to access all his articles through the author , for example user.articles
    author = db.relationship("User", backref="articles")


class UserExtension(db.Model):
    __tablename__ = 'user_extension'
    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    school = db.Column(db.String(100))
    user_id = db.Column(db.Integer, db.ForeignKey("user.id"))

    # db.backref
    # 1. In reverse application, you need to pass some other parameters , Then you need to use this function , If you don't need to use , As long as relationship Of backref Parameter , Just set the name of the back reference 
    # 2.uselist=False When it stands for back reference , It's not a list , It's an object , Only one can be found , one-on-one 
    user = db.relationship("User", backref=db.backref("extension", uselist=False))

if __name__ == '__main__':
    app.run()

Perform model migration
①flask db init
②flask db migrate
③flask db upgrade
The second step flask db migrate Can be written as flask db migrate -m "first commit", In this way, you can indicate what has been modified when migrating the script . The added comments will be reflected in the migration script

When ORM After the model is modified , For example, I give User Added a password Field , So how to migrate
, Don't... At this time init 了 , direct flask db migrate -m "add password",flask db upgrade that will do
Reference resources ：https://www.zlkt.net/book/detail/10/297