Models & Migrations

A Django model is a Python class that defines the structure of your data — each model maps to a single database table and each attribute maps to a column — and migrations are the version-controlled files Django generates to create and update those tables as your models change.

Learn Models & Migrations in our free Django course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick reference.

Part of the free Django course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

In this lesson you'll define your first model, learn the most common field types and their options, and master the makemigrations and migrate workflow that keeps your database in step with your code.

What You'll Learn in This Lesson

1 Defining a Model Class

A model lives in your app's models.py file. You subclass models.Model and declare each column as a class attribute set to a field instance. Here is a Post model with several common field types:

• CharField — short text; always needs max_length .
• TextField — large, unlimited-length text like article bodies.
• IntegerField — whole numbers such as counts.
• BooleanField — a true/false flag.
• DateTimeField — a date and time value.

The __str__ method tells Django (and the admin) how to display a single object. Without it, objects print as something unhelpful like Post object (1) .

2 Field Options

Every field accepts options that control how it behaves and what the database column allows. These are the ones you'll use constantly:

• max_length — required on CharField ; the column's character limit.
• null — if True , the database column may store NULL.
• blank — if True , the field may be left empty in forms and the admin.
• default — a value used when none is supplied.
• auto_now_add — set the timestamp once, when the row is first created.
• choices — restrict the value to a fixed list of options.

3 makemigrations & migrate

Writing a model in models.py does not change the database by itself. You take two steps: makemigrations writes a migration file describing the change, and migrate applies it to the database.

A generated migration file is plain Python. It records the operations Django will perform:

🎯 Your Turn: Complete the Field

A CharField always needs a max_length . Fill in the blank with the number 200 so the field definition is valid.

Common Errors (And How to Fix Them)

❌ Your models have changes that are not yet reflected in a migration

You edited a model but forgot to capture the change.

✅ Fix: run python manage.py makemigrations then python manage.py migrate .

❌ CharFields must define a 'max_length' attribute

A CharField was declared without a length limit.

✅ Fix: add a length, e.g. models.CharField(max_length=100) .

❌ You are trying to add a non-nullable field without a default

Adding a required field to a table that already has rows leaves them with no value.

✅ Fix: give the field a default= value, or make it null=True .

📋 Quick Reference

Field Type

What It Stores

CharField

Short text with a required max_length

TextField

Large, unlimited-length text

IntegerField

Whole numbers

BooleanField

A true/false flag

DateTimeField

A date and time value

🏆 Mini Challenge: Build a Product Model

Model a simple Product with a name, a price, and an in-stock flag, then print a readable summary using its __str__ method.

❓ Frequently Asked Questions

Lesson 7 complete — your data has a schema!

You can now define models with the core field types, tune their behaviour with options like null , blank , default , and choices , and keep your database in sync using makemigrations and migrate .

🚀 Up next: The ORM: Queries — learn how to create, read, filter, and update rows with Django's query API.

Practice quiz

Continue this course

• Previous: The Django Admin
• Next: The ORM: Queries