1. Setting Up Flask and Dependencies

Step 1: Install Required Packages

Ensure Flask and SQLAlchemy are installed:

pip install flask flask-sqlalchemy

2. Setting Up the Flask App and Database

Step 2: Initialize Flask and SQLAlchemy

Create a file app.py and set up the Flask application:

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

app = Flask(__name__)

# Configure SQLite Database
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///books.db"
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
db = SQLAlchemy(app)

3. Creating a Database Model

Step 3: Define the Book Model

class Book(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(100), nullable=False)
    author = db.Column(db.String(100), nullable=False)

    def to_dict(self):
        return {"id": self.id, "title": self.title, "author": self.author}

# Create database tables
with app.app_context():
    db.create_all()

4. Implementing CRUD Operations

Step 4: Create a New Book (POST Request)

@app.route("/books", methods=["POST"])
def add_book():
    data = request.get_json()
    new_book = Book(title=data["title"], author=data["author"])
    db.session.add(new_book)
    db.session.commit()
    return jsonify(new_book.to_dict()), 201

Use Postman or cURL to send a POST request with JSON data:

{
    "title": "Flask for Beginners",
    "author": "John Doe"
}

Step 5: Get All Books (GET Request)

@app.route("/books", methods=["GET"])
def get_books():
    books = Book.query.all()
    return jsonify([book.to_dict() for book in books])

Step 6: Get a Single Book by ID

@app.route("/books/<int:book_id>", methods=["GET"])
def get_book(book_id):
    book = Book.query.get(book_id)
    return jsonify(book.to_dict()) if book else jsonify({"error": "Book not found"}), 404

Step 7: Update an Existing Book (PUT Request)

@app.route("/books/<int:book_id>", methods=["PUT"])
def update_book(book_id):
    book = Book.query.get(book_id)
    if not book:
        return jsonify({"error": "Book not found"}), 404

    data = request.get_json()
    book.title = data.get("title", book.title)
    book.author = data.get("author", book.author)
    db.session.commit()
    return jsonify(book.to_dict())

Step 8: Delete a Book (DELETE Request)

@app.route("/books/<int:book_id>", methods=["DELETE"])
def delete_book(book_id):
    book = Book.query.get(book_id)
    if not book:
        return jsonify({"error": "Book not found"}), 404

    db.session.delete(book)
    db.session.commit()
    return jsonify({"message": "Book deleted successfully"})

5. Running and Testing the Application

• Run the Flask app:

python app.py

Conclusion

In this guide, you learned how to:

✅ Set up a Flask CRUD API with SQLite
✅ Implement POST, GET, PUT, DELETE requests
✅ Use Flask-SQLAlchemy for database management
✅ Handle errors and return JSON responses

You can extend this app by adding user authentication, pagination, and better error handling. 🚀