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Published on August 04, 2024By DeveloperBreeze

Tutorial: Build a Web Application with Flask and PostgreSQL

In this tutorial, you'll learn how to build a web application using the Flask framework and PostgreSQL as the database. We'll cover the entire process, from setting up your environment to deploying your application.

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Prerequisites

  • Python Installed: Ensure Python 3.x is installed on your system.

  • Pip Package Manager: Ensure pip is installed for managing Python packages.

  • PostgreSQL: Install PostgreSQL and set up a database for your application.

  • Basic Python and SQL Knowledge: Familiarity with Python and SQL basics will be helpful.

Step 1: Set Up Your Development Environment

    • Create a Virtual Environment: It's a good practice to use a virtual environment for your project to manage dependencies. 

python -m venv venv

    • Activate the Virtual Environment:

- Windows:

.\venv\Scripts\activate

- macOS/Linux:

source venv/bin/activate

    • Install Required Packages: Install Flask, SQLAlchemy, and psycopg2 for PostgreSQL integration. 

pip install Flask SQLAlchemy psycopg2-binary

Step 2: Create a Basic Flask Application

    • Create the Project Structure: 

mkdir flask_app
   cd flask_app

    • Create the Flask Application: Create a file named app.py and add the following code. 

from flask import Flask, render_template, request, redirect, url_for
   from flask_sqlalchemy import SQLAlchemy

   app = Flask(__name__)
   app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://username:password@localhost:5432/mydatabase'
   app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
   db = SQLAlchemy(app)

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

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

   @app.route('/')
   def index():
       users = User.query.all()
       return render_template('index.html', users=users)

   @app.route('/add', methods=['POST'])
   def add_user():
       username = request.form['username']
       email = request.form['email']
       new_user = User(username=username, email=email)
       db.session.add(new_user)
       db.session.commit()
       return redirect(url_for('index'))

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

    • Create HTML Template: Create a directory named templates and add a file named index.html with the following content: 

<!DOCTYPE html>
   <html lang="en">
   <head>
       <meta charset="UTF-8">
       <meta name="viewport" content="width=device-width, initial-scale=1.0">
       <title>Flask App</title>
   </head>
   <body>
       <h1>User List</h1>
       <ul>
           {% for user in users %}
           <li>{{ user.username }} - {{ user.email }}</li>
           {% endfor %}
       </ul>

       <h2>Add User</h2>
       <form action="{{ url_for('add_user') }}" method="post">
           <label for="username">Username:</label>
           <input type="text" id="username" name="username" required>
           <label for="email">Email:</label>
           <input type="email" id="email" name="email" required>
           <button type="submit">Add User</button>
       </form>
   </body>
   </html>

Step 3: Set Up PostgreSQL

    • Create a Database: Log in to your PostgreSQL instance and create a new database. 

CREATE DATABASE mydatabase;

    • Create a Database User: Create a new user with privileges on the database. 

CREATE USER myuser WITH PASSWORD 'mypassword';
   GRANT ALL PRIVILEGES ON DATABASE mydatabase TO myuser;

    • Update Database URI: In app.py, replace 'username:password@localhost:5432/mydatabase' with your actual database username, password, host, port, and database name.

Step 4: Initialize the Database

    • Create the Database Tables: Run the following commands in a Python shell to create the database tables. 

from app import db
   db.create_all()

    • Start the Flask Application: Run the application. 

python app.py

    • Access the Application: Open your web browser and go to http://127.0.0.1:5000/. You should see the user list and a form to add new users.

Step 5: Perform CRUD Operations

  • Create: Add new users using the form on the homepage.

  • Read: View the list of users on the homepage.

  • Update and Delete: You can extend the application to include update and delete functionality by adding new routes and templates.

Step 6: Deploy the Application

    • Choose a Hosting Platform: Select a platform such as Heroku, AWS, or Google Cloud to host your Flask application.

    • Prepare for Deployment: Create a Procfile and requirements.txt to specify dependencies and deployment instructions.

- Procfile:

web: python app.py

- requirements.txt: List your dependencies.

Flask
     SQLAlchemy
     psycopg2-binary
     gunicorn

    • Deploy: Follow the hosting platform's instructions to deploy your application.

Conclusion

In this tutorial, you built a basic web application using Flask and PostgreSQL. You learned how to set up your environment, create and interact with a PostgreSQL database using SQLAlchemy, and perform basic CRUD operations. You also prepared your application for deployment on a hosting platform.

For further improvements, consider adding authentication, user input validation, and advanced database queries. You can also explore deploying your app with Docker for a more portable deployment solution.

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