Database migration in deployment in Flask - Mini Project: Build & Apply

Database migration in deployment with Flask

📖 Scenario: You are building a Flask web app that stores user data in a database. When you update your app, you need to change the database structure without losing existing data. This process is called database migration.In this project, you will set up a simple Flask app with a database, configure migration support, create a migration script, and apply the migration to update the database.

🎯 Goal: Build a Flask app that uses Flask-Migrate to handle database migrations during deployment. You will create the initial database, configure migration settings, generate a migration script, and apply it to update the database schema safely.

📋 What You'll Learn

Use Flask with SQLAlchemy for database handling

Use Flask-Migrate to manage database migrations

Create an initial User model with id and name fields

Add a new email field to the User model via migration

Apply migration commands programmatically in the app

💡 Why This Matters

🌍 Real World

Database migrations are essential when deploying updates to web apps that use databases. They help change the database structure safely without losing user data.

💼 Career

Knowing how to manage database migrations with Flask and Flask-Migrate is a key skill for backend developers working on web applications that evolve over time.

1

Set up Flask app and initial User model

Create a Flask app instance called app. Set up SQLAlchemy with db = SQLAlchemy(app). Define a User model with id as an integer primary key and name as a string column. Initialize the database with db.create_all().

Flask

# Create Flask app, SQLAlchemy db, and User model
# Your code here

Need a hint?

Remember to import Flask and SQLAlchemy. Set the database URI to a local SQLite file. Define the User model with id and name columns. Call db.create_all() inside the app context.

2

Configure Flask-Migrate for migration support

Import Migrate from flask_migrate. Create a migrate object with migrate = Migrate(app, db) to enable migration support in your Flask app.

Flask

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

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False

db = SQLAlchemy(app)

migrate = Migrate(app, db)  # Add migration support

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), nullable=False)

with app.app_context():
    db.create_all()

Need a hint?

Import Migrate and create a migrate object passing app and db.

3

Add new email field to User model for migration

Modify the User model by adding a new column email as a string with max length 120 and allow null values. Do not remove existing fields.

Flask

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

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False

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

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), nullable=False)
    # Add email column below

with app.app_context():
    db.create_all()

Need a hint?

Add email = db.Column(db.String(120), nullable=True) inside the User model.

4

Apply migration commands programmatically

Import upgrade from flask_migrate. Inside the app context, call upgrade() to apply the migration and update the database schema with the new email column.

Flask

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

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False

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

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), nullable=False)
    email = db.Column(db.String(120), nullable=True)

with app.app_context():
    db.create_all()
    # Apply migration upgrade
    # Your code here

Need a hint?

Import upgrade and call it inside the app context to apply migrations.