Using SQLAlchemy

So far, you used raw SQL to work with your database.

Now you will use SQLAlchemy to make this easier and integrate it into your Flask app.

What is SQLAlchemy?

SQLAlchemy lets you work with databases using Python instead of writing SQL manually.

Step 1: Create a New Project Folder

In your terminal:

mkdir flask-db-app
cd flask-db-app

Step 2: Create a Virtual Environment

python -m venv venv

Step 3: Activate the Environment

On macOS/Linux:

source venv/bin/activate

On Windows:

venv\Scripts\activate

You should now see (venv) in your terminal.

Step 4: Install Required Packages

pip install flask flask-sqlalchemy

Step 5: Create Project Files

Create these files:

touch app.py models.py

Step 6: Setup Flask App

Open app.py:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)

app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///database.db"
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False

db = SQLAlchemy(app)

@app.route("/")
def home():
    return "App is running"

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

Step 7: Create a Model

Open models.py:

from app import db

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(100))

Step 8: Create the Database

Open Python shell:

python

Then run:

from app import db
from models import User

db.create_all()

Exit:

exit()

Step 9: Insert Data

Open Python again:

python

from app import db
from models import User

user = User(name="Alice")

db.session.add(user)
db.session.commit()

Step 10: Query Data

users = User.query.all()

for user in users:
    print(user.name)

You should see:

Alice

How It Works

• Models represent tables
• Python objects represent rows
• SQLAlchemy handles SQL automatically

Why This Matters

You now:

• Work with Python instead of SQL
• Integrate database into Flask
• Build real applications

Common Mistakes

• ❌ Forgetting to activate virtual environment
• ❌ Not importing models before create_all()
• ❌ Forgetting commit()
• ❌ Running commands outside project folder

Summary

• You created a Flask project
• You set up SQLAlchemy
• You created a model
• You inserted and queried data

In the next lesson, you will build a full application using a database.