Part 1: Setting up the project

import os

class Config:
    SQLALCHEMY_DATABASE_URI = os.getenv('DATABASE_URL', 'sqlite:///app.db')  # Use SQLite by default
    SQLALCHEMY_TRACK_MODIFICATIONS = False  # Disable modification tracking

This code defines a Config class that manages database settings for a Flask application. It imports the os module to access environment variables and sets SQLALCHEMY_DATABASE_URI to the value of the DATABASE_URL environment variable, defaulting to an SQLite database file (app.db) if the variable is not set. Additionally, it disables SQLAlchemy’s modification tracking by setting SQLALCHEMY_TRACK_MODIFICATIONS to False, which improves performance by reducing unnecessary overhead.

Step 6: Add a basic route

In app/routes.py, add the following code:

from flask import Blueprint, jsonify

bp = Blueprint('api', __name__, url_prefix='/api')

@bp.route('/test', methods=['GET'])
def test():
    return jsonify({"message": "Welcome to the user management microservice"})

This code creates an API blueprint for a Flask application and defines a test route. It imports Blueprint and jsonify from Flask, then initializes a blueprint named api with a URL prefix of /api. The test function handles GET requests at /api/test and returns a JSON response containing a welcome message.

Step 7: Initialize the Flask application

In app/__init__.py, initialize the Flask app and SQLAlchemy:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from config import Config

db = SQLAlchemy()

def create_app():
    app = Flask(__name__)
    app.config.from_object(Config)

    db.init_app(app)

    with app.app_context():
        from . import routes
        app.register_blueprint(routes.bp)

        db.create_all()

    return app

This code sets up a Flask application with SQLAlchemy for database management. It imports the necessary modules and initializes an SQLAlchemy instance (db). The create_app function creates a Flask app, loads configuration settings from the Config class, and initializes the database with the app. Inside the application context, it imports routes from the current package, registers them as a blueprint, and creates any missing database tables. Finally, the function returns the configured Flask application.

Step 8: Define the database model

In app/models.py, define the User model:

from . import db

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)
    password_hash = db.Column(db.String(128), nullable=False)

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

This code defines a User model for a Flask application using SQLAlchemy. It imports the database instance (db) and creates the User class, which inherits from db.Model. The class defines four columns: id as the primary key, username as a unique and required string of up to 80 characters, email as a unique and required string of up to 120 characters, and password_hash as a required string of up to 128 characters. The __repr__ method returns a string representation of the user, displaying the username.