models.py

models.py#

What is models.py?#

models.py defines the structure of your database using Python classes, allowing Django to automatically create, update, and manage database tables through migrations.

In Django:

  • You do not write SQL directly

  • You define Models

  • Django creates tables automatically

Think of it as:

Python classes → Database tables

Mental Model#

Django

Database

Model class

Table

Model field

Column

Model instance

Row

ForeignKey

Relationship

Migration

SQL version control

Basic structure of models.py#

from django.db import models

This imports Django’s ORM (Object-Relational Mapper).

Small example

1️⃣ Define a model

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimalField(max_digits=8, decimal_places=2)
    created_at = models.DateTimeField(auto_now_add=True)

What happens?

Line

Meaning

class Product

Table name: product

models.Model

Base ORM class

CharField

VARCHAR

DecimalField

DECIMAL

DateTimeField

TIMESTAMP

2️⃣ Django auto-generates SQL

You never write:

CREATE TABLE product (...)

Django does it via migrations.

Models → Migrations → Database

The lifecycle:

models.py
  ↓
makemigrations
  ↓
migration files
  ↓
migrate
  ↓
database tables

Field Types (core ones)#

Field

Use

CharField

Short text

TextField

Long text

IntegerField

Numbers

BooleanField

True/False

DateTimeField

Dates

ForeignKey

Relations

ManyToManyField

Many-to-many

Check out this list for more field types.

🔗 Relationships

ForeignKey (One-to-Many)

class Order(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
Meaning:

  • One product → many orders

ManyToManyField (Many-to-Many)

class Student(models.Model):
    courses = models.ManyToManyField("Course")
Naming rules (best practice):

  • ✔ Singular model names

  • ✔ CamelCase class names

  • ✔ snake_case field names

Good:

class UserProfile(models.Model):

Bad:

class users(models.Model):

__str__() (important for admin)

def __str__(self):
    return self.name
This controls:

  • Admin display

  • Debugging

  • Django shell readability

Meta options (advanced but important)

class Product(models.Model):
    name = models.CharField(max_length=100)
    class Meta:
        ordering = ["-created_at"]
        db_table = "products"

How models connect to other files

File

Relation

models.py

Defines schema

admin.py

Displays models

views.py

Reads/writes models

serializers.py

(DRF) API layer

migrations/

DB versioning
Common beginner mistakes:

  • Editing migration files manually

  • Forgetting makemigrations

  • Changing models without migrating

  • Importing models incorrectly

Real-world analogy

Think of models.py as:

Architectural blueprint of a building

If you change the blueprint → rebuild (migrate)

Practice on Models:
Contents