Django Models

Defining a Model

A model is a Python class that subclasses django.db.models.Model. Each class attribute is a Field instance that maps to a database column, and Django uses the class as a whole to generate the table's schema.

from django.db import models

class Product(models.Model):
    name = models.CharField(max_length=200)
    price = models.DecimalField(max_digits=8, decimal_places=2)
    in_stock = models.BooleanField(default=True)
    created_at = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return self.name

Common Field Types

• CharField(max_length=...) - short text like names or titles
• TextField() - long, unbounded text such as descriptions
• IntegerField() / DecimalField() - whole numbers or precise decimals like prices
• BooleanField(default=...) - true/false flags
• DateTimeField(auto_now_add=True) - a timestamp set once when the row is created
• ForeignKey(Model, on_delete=...) - a many-to-one relationship to another model

class Review(models.Model):
    product = models.ForeignKey(
        Product,
        on_delete=models.CASCADE,
        related_name='reviews',
    )
    rating = models.IntegerField()
    comment = models.TextField(blank=True)

    def __str__(self):
        return f'{self.rating} stars for {self.product.name}'

Migrations

Migrations are how Django keeps your database schema in sync with your models. makemigrations inspects your model classes, compares them to the last known state, and writes a migration file describing the difference. migrate then applies any pending migration files to the actual database.

# Generate migration files from model changes
python manage.py makemigrations

# Apply pending migrations to the database
python manage.py migrate