Flask Blueprint CRUD (via API)

Here's a basic example of a CRUD Flask application using a single Blueprint and MySQL. Please note that we'll use Flask-SQLAlchemy for ORM and Flask-Marshmallow for request validation and serialization.

Please, install necessary packages:

Here's the code:

from flask import Flask, request, Blueprint, jsonify
from flask_sqlalchemy import SQLAlchemy
from flask_marshmallow import Marshmallow

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://username:password@localhost/dbname'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False

db = SQLAlchemy(app)
ma = Marshmallow(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True)
    usernumber = db.Column(db.String(20), unique=True)
    comment = db.Column(db.String(200))

    def __init__(self, username, usernumber, comment):
        self.username = username
        self.usernumber = usernumber
        self.comment = comment

class UserSchema(ma.SQLAlchemyAutoSchema):
    class Meta:
        model = User
        load_instance = True

user_schema = UserSchema()
users_schema = UserSchema(many=True)

bp = Blueprint('user_api', __name__)

@bp.route('/user', methods=['POST'])
def add_user():
    username = request.json['username']
    usernumber = request.json['usernumber']
    comment = request.json['comment']
    new_user = User(username, usernumber, comment)
    db.session.add(new_user)
    db.session.commit()
    return user_schema.jsonify(new_user)

@bp.route('/user', methods=['GET'])
def get_users():
    all_users = User.query.all()
    result = users_schema.dump(all_users)
    return jsonify(result)

@bp.route('/user/<id>', methods=['GET'])
def get_user(id):
    user = User.query.get(id)
    return user_schema.jsonify(user)

@bp.route('/user/<id>', methods=['PUT'])
def update_user(id):
    user = User.query.get(id)
    username = request.json['username']
    usernumber = request.json['usernumber']
    comment = request.json['comment']
    user.username = username
    user.usernumber = usernumber
    user.comment = comment
    db.session.commit()
    return user_schema.jsonify(user)

@bp.route('/user/<id>', methods=['DELETE'])
def delete_user(id):
    user = User.query.get(id)
    db.session.delete(user)
    db.session.commit()
    return user_schema.jsonify(user)

app.register_blueprint(bp, url_prefix='/api')

if __name__ == '__main__':
    app.run(debug=True)

• POST /api/user: Create a new user.
• GET /api/user: Retrieve a list of all users.
• GET /api/user/<id>: Retrieve a single user by ID.
• PUT /api/user/<id>: Update a user by ID.
• DELETE /api/user/<id>: Delete a user by ID.

Note:

1. This is a very basic CRUD application and doesn't have any security measures. In a real-world application, you would want to add authentication, input sanitization, error handling, etc.
2. Replace 'mysql://username:password@localhost/dbname' with your MySQL database details.
3. Also, don't forget to run the DB (Xampp)
   

Instead of creating a REST API, we could adapt the example to be a simple web application with HTML templates for the user interface.

We will use Flask's built-in render_template function to serve HTML files and redirect function to redirect users to different routes.

Let's say we have an HTML file named index.html in a templates folder, and it's set up to display a list of users and a form to create a new user. We could render that file from our get_users route like so:

from flask import render_template, redirect, url_for, flash

# ...

@bp.route('/users', methods=['GET', 'POST'])
def users():
    if request.method == 'POST':
        username = request.form['username']
        usernumber = request.form['usernumber']
        comment = request.form['comment']
        new_user = User(username, usernumber, comment)
        db.session.add(new_user)
        db.session.commit()
        flash('User added successfully!', 'success')
        return redirect(url_for('users'))
    
    all_users = User.query.all()
    return render_template('index.html', users=all_users)

In this code, we've combined the create and list users functionality into one route. If the request method is POST, we create a new user. Otherwise, we display all users.

Here's how you might handle the update and delete functionality:

@bp.route('/user/update/<id>', methods=['GET', 'POST'])
def update_user(id):
    user = User.query.get(id)
    
    if request.method == 'POST':
        user.username = request.form['username']
        user.usernumber = request.form['usernumber']
        user.comment = request.form['comment']
        db.session.commit()
        flash('User updated successfully!', 'success')
        return redirect(url_for('users'))
    
    return render_template('update.html', user=user)

@bp.route('/user/delete/<id>', methods=['POST'])
def delete_user(id):
    user = User.query.get(id)
    db.session.delete(user)
    db.session.commit()
    flash('User deleted successfully!', 'success')
    return redirect(url_for('users'))

In update_user, if the request method is POST, we update the user. Otherwise, we display the current user data in a form for editing. In delete_user, we simply delete the user and then redirect the client back to the users list.

Note that flash function is used to display one-time notifications to the user.

You'll need to create index.html and update.html templates with the necessary forms for creating, updating and deleting users. For security reasons, ensure you protect against Cross Site Request Forgery (CSRF) in your forms. Flask-WTF and Flask-SeaSurf are some of the libraries that provide CSRF protection.

Again, remember that this is a very basic example. In a real-world application, you would want to add proper error handling, form validation, and user authentication.

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