Flask and Flask-SQLAlchemy Integration Examples

Flask is a lightweight web framework that allows you to build web applications quickly and efficiently. When paired with Flask-SQLAlchemy, a powerful extension that simplifies database interactions, you can manage your data with ease. Here, we’ll explore three diverse examples of integrating Flask with Flask-SQLAlchemy that demonstrate how to create, read, update, and delete data in a database.

Example 1: Creating a Simple User Registration System

Context

In this example, we’ll create a simple user registration system where users can sign up with their name and email. This will help you understand how to set up a basic database model and create entries in the database.

from flask import Flask, request, jsonify
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///users.db'
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(50), nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)

    def __repr__(self):
        return f'<User {self.name}>'

@app.route('/register', methods=['POST'])
def register():
    data = request.get_json()
    new_user = User(name=data['name'], email=data['email'])
    db.session.add(new_user)
    db.session.commit()
    return jsonify({'message': 'User registered!'}), 201

if __name__ == '__main__':
    db.create_all()  # Create the database
    app.run(debug=True)

Notes

• Make sure to send a POST request to /register with JSON data containing name and email.
• This example uses SQLite for simplicity, but you can use other databases like PostgreSQL or MySQL with minor adjustments to the connection string.

Example 2: Querying and Displaying User Data

Context

Now, let’s build on our previous example by allowing users to view all registered users. This showcases how to query data from the database and return it in a readable format.

@app.route('/users', methods=['GET'])
def get_users():
    users = User.query.all()  # Query all users
    output = []
    for user in users:
        user_data = {'id': user.id, 'name': user.name, 'email': user.email}
        output.append(user_data)
    return jsonify({'users': output})

Notes

• This code snippet should be added to the same Flask application as the previous example.
• When you send a GET request to /users, it will return a JSON array of all registered users.
• This is a great way to see how data can be retrieved from your database.

Example 3: Updating and Deleting User Records

Context

In our final example, we will implement functionality to update and delete user records. This will demonstrate how to modify existing data in the database and remove it as needed.

@app.route('/user/<int:user_id>', methods=['PUT', 'DELETE'])
def manage_user(user_id):
    user = User.query.get(user_id)
    if request.method == 'PUT':  # Update user
        data = request.get_json()
        user.name = data.get('name', user.name)
        user.email = data.get('email', user.email)
        db.session.commit()
        return jsonify({'message': 'User updated!'}), 200
    elif request.method == 'DELETE':  # Delete user
        db.session.delete(user)
        db.session.commit()
        return jsonify({'message': 'User deleted!'}), 200
    return jsonify({'message': 'User not found!'}), 404

Notes

• To update a user, send a PUT request to /user/<user_id> with the JSON data you want to update.
• To delete a user, send a DELETE request to the same endpoint.
• Ensure you provide a valid user ID.

Conclusion

These examples of integrating Flask with Flask-SQLAlchemy provide a foundational understanding of how to work with databases in your Flask applications. Whether you’re creating, reading, updating, or deleting records, Flask-SQLAlchemy makes it much easier to manage your data effectively.