Setting Up a Database in Flask

Key Concepts

• Database Management Systems (DBMS)
• Object-Relational Mapping (ORM)
• Flask-SQLAlchemy
• Database Models
• Database Operations

1. Database Management Systems (DBMS)

A Database Management System (DBMS) is software that allows users to define, create, maintain, and control access to the database. Common DBMS include MySQL, PostgreSQL, SQLite, and MongoDB.

2. Object-Relational Mapping (ORM)

Object-Relational Mapping (ORM) is a technique that lets you query and manipulate data from a database using an object-oriented paradigm. ORM libraries, like SQLAlchemy, map database tables to Python classes and their instances.

3. Flask-SQLAlchemy

Flask-SQLAlchemy is an extension for Flask that simplifies the use of SQLAlchemy within Flask applications. It provides a simple interface to configure and interact with databases.

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///mydatabase.db'
db = SQLAlchemy(app)
    

4. Database Models

Database models are Python classes that represent database tables. Each attribute of the class corresponds to a column in the table. Models define the structure and relationships of the data.

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)

    def __repr__(self):
        return f'User({self.username}, {self.email})'
    

5. Database Operations

Database operations include creating, reading, updating, and deleting (CRUD) records. Flask-SQLAlchemy provides methods to perform these operations seamlessly.

# Create a new user
new_user = User(username='john_doe', email='john@example.com')
db.session.add(new_user)
db.session.commit()

# Read users
users = User.query.all()

# Update a user
user = User.query.filter_by(username='john_doe').first()
user.email = 'john.doe@example.com'
db.session.commit()

# Delete a user
user = User.query.filter_by(username='john_doe').first()
db.session.delete(user)
db.session.commit()