{"id":12140,"date":"2020-02-13T06:31:15","date_gmt":"2020-02-13T11:31:15","guid":{"rendered":"https:\/\/qxf2.com\/blog\/?p=12140"},"modified":"2020-02-13T06:31:15","modified_gmt":"2020-02-13T11:31:15","slug":"database-migration-flask-migrate","status":"publish","type":"post","link":"https:\/\/qxf2.com\/blog\/database-migration-flask-migrate\/","title":{"rendered":"Getting started with Database Schema Migration (Flask-Migrate)"},"content":{"rendered":"

Why this post?<\/h3>\n

This post helps you to quickly setup and get started with Database schema Migration using Flask-Migrate.
\nFor example if you already had created a database that contains some tables and now if you add a new column to one of the table and then if you want to revert it to the previous state, it\u2019s difficult to do so. This is when the database migration comes in handy, as it keeps a track of database schema changes for you, and one can easily traverse back to an older or newer version of the database.<\/p>\n

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What is Database Schema migration?<\/h3>\n

Database schema migration<\/b> refers to the managing of incremental, reversible changes and version control to the relational database schema. A schema migration is performed on a database whenever it is necessary to update or revert that database’s schema to some newer or older version.<\/p>\n

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What is Flask-Migrate?<\/h3>\n

Flask-Migrate<\/a> is a wrapper around Alembic, which handles SQLAlchemy database migrations for Flask applications. To be explicit, the use of the Flask-Migrate module is intended for Flask applications that are using SQLAlchemy.<\/p>\n

Alembic<\/a> is a lightweight database migration tool for usage with the SQLAlchemy Database Toolkit for Python.<\/p>\n

SQLAlchemy<\/a> is the Python SQL toolkit and Object Relational Mapper that gives application developers the full power and flexibility of SQL.<\/p>\n

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Setup of Flask-Migrate<\/h3>\n

Install Flask withpip<\/code>:<\/p>\n

pip install Flask\r\n<\/pre>\n
Install Flask-Migrate with pip<\/code>:<\/p>\n
pip install Flask-Migrate\r\n<\/pre>\n
Install Flask-Script withpip<\/code>:<\/p>\n
pip install Flask-Script\r\n<\/pre>\n
Install flask-sqlalchemy withpip<\/code>:<\/p>\n
pip install flask-sqlalchemy\r\n<\/pre>\n
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This is an example application that handles database migrations through Flask-Migrate:<\/p>\n
from flask import Flask\r\nfrom flask_sqlalchemy import SQLAlchemy\r\nfrom flask_script import Manager\r\nfrom flask_migrate import Migrate, MigrateCommand\r\n\r\napp = Flask(__name__)\r\napp.config[\"SQLALCHEMY_DATABASE_URI\"] = \"sqlite:\/\/\/data.db\"\r\ndb = SQLAlchemy(app)\r\nmigrate=Migrate(app,db) #Initializing migrate.\r\nmanager = Manager(app)\r\nmanager.add_command('db',MigrateCommand)\r\n\r\nclass Employee(db.Model):\r\n    id = db.Column(db.Integer, primary_key=True)\r\n    name = db.Column(db.String, unique=True, nullable=False)\r\n    email = db.Column(db.String, unique=True, nullable=False)\r\n\r\nclass Company(db.Model):\r\n    cid = db.Column(db.Integer, primary_key=True)\r\n    cname = db.Column(db.String, unique=True, nullable=False)\r\n    clocation = db.Column(db.String, unique=False, nullable=False)\r\n\r\nif __name__ == \"__main__\":\r\n     manager.run() \r\n<\/pre>\n
Note:- Calling manager.run() prepares your Manager instance to receive input from the command line.<\/strong><\/p>\n
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We need to run the code using python. The code has been saved as\u00a0migrate_example.py <\/strong>file.<\/p>\n
We will use some basic commands:-<\/h3>\n