**Course Title:** Mastering Flask Framework: Building Modern Web Applications **Section Title:** Working with Databases: SQLAlchemy **Topic:** Set up a database for a Flask application, perform CRUD operations using SQLAlchemy.(Lab topic) ### Overview In this lab topic, we will set up a database for a Flask application using SQLAlchemy and perform basic CRUD (Create, Read, Update, Delete) operations on it. By the end of this lab, you will have hands-on experience with database operations using SQLAlchemy in a Flask application. ### Prerequisites Before proceeding with this lab, make sure you have completed the following topics: * Introduction to Flask and Development Environment * Routing, Views, and Templates * Working with Databases: SQLAlchemy Ensure that you have Flask, Flask-SQLAlchemy, and Flask-Migrate installed in your virtual environment. ### Step 1: Create a New Flask Application Create a new directory for your lab and create a new virtual environment using the following command: ```bash python -m venv venv ``` Activate your virtual environment and install the required packages: ```bash # Install Flask, Flask-SQLAlchemy, and Flask-Migrate pip install flask flask-SQLAlchemy flask-Migrate ``` Create a new file called `app.py` and initialize a new Flask application: ```python from flask import Flask from flask_sqlalchemy import SQLAlchemy from flask_migrate import Migrate app = Flask(__name__) # Initialize the database app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///mydatabase.db' app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False db = SQLAlchemy(app) # Initialize the migration migrate = Migrate(app, db) from . import routes, models ``` Create a new file called `models.py` to define your database models: ```python from app import db 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(80), nullable=False, unique=True) def __repr__(self): return '<User %r>' % self.name def __init__(self, name, email): self.name = name self.email = email ``` ### Step 2: Create the Database Tables Run the following commands to create the database tables: ``` # Create the migration scripts flask db init # Create the tables flask db migrate -m "create tables" flask db upgrade ``` ### Step 3: Perform CRUD Operations Create a new file called `routes.py` to define routes for the CRUD operations: ```python from app import app, db from .models import User from flask import jsonify, request # Route to create a new user @app.route('/users', methods=['POST']) def create_user(): data = request.get_json() new_user = User(name=data['name'], email=data['email']) db.session.add(new_user) db.session.commit() return jsonify({'message' : 'New user created!'}) # Route to get all users @app.route('/users', methods=['GET']) def get_users(): users = User.query.all() output = [] for user in users: user_data = {'id' : user.id, 'name' : user.name, 'email' : user.email} output.append(user_data) return jsonify({'users' : output}) # Route to get one user @app.route('/users/<id>', methods=['GET']) def get_user(id): user = User.query.get(id) if user is None: return jsonify({'message' : 'User not found!'}) user_data = {'id' : user.id, 'name' : user.name, 'email' : user.email} return jsonify({'user' : user_data}) # Route to update a user @app.route('/users/<id>', methods=['PUT']) def update_user(id): user = User.query.get(id) if user is None: return jsonify({'message' : 'User not found!'}) data = request.get_json() user.name = data['name'] user.email = data['email'] db.session.commit() return jsonify({'message' : 'User updated!'}) # Route to delete a user @app.route('/users/<id>', methods=['DELETE']) def delete_user(id): user = User.query.get(id) if user is None: return jsonify({'message' : 'User not found!'}) db.session.delete(user) db.session.commit() return jsonify({'message' : 'User deleted!'}) ``` ### Step 4: Run the Flask Application Finally, run the Flask application using the following command: ```bash python app.py ``` You can now use a tool like Postman or curl to test the CRUD operations on your database. **Lab Tasks:** 1. Test the CRUD operations on your database using Postman or curl. 2. Add validation to your API endpoints to handle invalid data. 3. Implement pagination to limit the number of users returned in the GET /users endpoint. 4. Use error handling to catch and return errors that occur during database operations. 5. Expand your API to include additional endpoints and features. **Resources:** * [Flask-SQLAlchemy Documentation](https://flask-sqlalchemy.palletsprojects.com/en/2.x/) * [Flask-Migrate Documentation](https://flask-migrate.readthedocs.io/en/latest/) * [SQLAlchemy Documentation](https://www.sqlalchemy.org/library.html) After completing this lab, you will have gained hands-on experience with setting up a database for a Flask application and performing CRUD operations using SQLAlchemy. What's Next? In the next topic, we will cover implementing user registration, login, and logout using Flask-Security.