basic-models.md

Basic Models in Flask-SQLAlchemy

In Flask-SQLAlchemy, models are Python classes that represent database tables. Below is a step-by-step guide on how to create and define models.

Step 1: Create a Model Class

• Models in Flask-SQLAlchemy inherit from db.Model.
• Each attribute of the class corresponds to a column in the database table.

Example Model Definition

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

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

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}>'

if __name__ == '__main__':
    db.create_all()
    print("Database and tables created!")

Key Components Explained

1. db.Model Inheritance

• All models inherit from db.Model to connect them to the SQLAlchemy instance.

2. Columns (db.Column)

• Define the fields of the table.
• Each column has a data type and optional constraints.

Common Data Types

• db.Integer: Integer values.
• db.String: Variable-length string.
• db.Float: Floating-point numbers.
• db.Boolean: Boolean values.
• db.DateTime: Date and time values.
• db.Text: Large text fields.

Constraints

• primary_key=True: Marks the column as the primary key.
• unique=True: Ensures unique values for the column.
• nullable=False: Makes the column non-nullable.

Creating the Database

To create the database and tables, use:

if __name__ == '__main__':
    db.create_all()

This will generate the necessary tables in the database.

Conclusion

This is a basic example of setting up models in Flask-SQLAlchemy. In the next guide, we will cover column attributes in detail, including default values, indexing, and relationships between tables.