Introduction

So far, you’ve used Django models mainly to define database structure. But models can do much more than just store data — they can also contain logic.

Django allows you to add:

methods → functions inside your model
properties → computed attributes (like virtual fields)

This makes your models smarter, cleaner, and easier to maintain.

Instead of spreading logic across views and templates, you can centralize it inside your models — which is a best practice in Django.

What You Will Learn

By the end of this tutorial, you will understand:

what model methods are
what model properties are
how to define custom methods
how to use @property
how to use model methods in templates
how to organize business logic inside models
best practices for clean Django code

Prerequisites

You should already know:

Django models
QuerySets and ORM
relationships (ForeignKey, etc.)
basic templates

1. What Are Model Methods?

A model method is simply a Python function defined inside a Django model.

It allows you to:

add behavior to your model
compute values
encapsulate business logic
keep views and templates clean

2. Basic Example of a Model Method

`models.py`

from django.db import models

class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()

    def short_content(self):
        return self.content[:50]

Usage in Python

post = Post.objects.first()
print(post.short_content())

Usage in Template

<p>{{ post.short_content }}</p>

👉 In templates, you don’t need parentheses.

3. The Special `str()` Method

You already used this, but it’s actually a model method.

def __str__(self):
    return self.title

It defines how the object appears:

in Django admin
in shell
in debugging

Always include a meaningful __str__() method.

4. Model Methods with Logic

Model methods can contain real logic.

Example

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.FloatField()
    discount = models.FloatField(default=0)

    def final_price(self):
        return self.price - (self.price * self.discount / 100)

Usage

product.final_price()

Template

<p>Price: {{ product.final_price }}</p>

5. What Are Model Properties?

A property is a method that behaves like an attribute.

You define it using the @property decorator.

6. Example of `@property`

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.FloatField()
    discount = models.FloatField(default=0)

    @property
    def final_price(self):
        return self.price - (self.price * self.discount / 100)

Usage

product.final_price   # no parentheses

Template

<p>{{ product.final_price }}</p>

7. Method vs Property

Feature	Method	Property
Syntax	`obj.method()`	`obj.property`
Use case	action / logic	computed value
Template usage	no parentheses	no parentheses

👉 Rule of thumb:

use methods when action is involved
use properties for calculated values

8. Real Example: Blog Model

from django.db import models
from django.utils.text import slugify

class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)

    def get_summary(self):
        return self.content[:100]

    @property
    def is_long(self):
        return len(self.content) > 500

    def save(self, *args, **kwargs):
        self.slug = slugify(self.title)
        super().save(*args, **kwargs)

Usage

post.get_summary()
post.is_long

9. Using Model Methods in Templates

Django templates allow you to use model methods directly.

<h2>{{ post.title }}</h2>
<p>{{ post.get_summary }}</p>

{% if post.is_long %}
    <p>This is a long article</p>
{% endif %}

10. Model Methods with Relationships

Model methods become even more powerful when used with relationships.

Example

class Category(models.Model):
    name = models.CharField(max_length=100)

    def post_count(self):
        return self.posts.count()

👉 assuming:

related_name='posts'

Usage

category.post_count()

Template

<p>Posts: {{ category.post_count }}</p>

11. Computed Fields Example

class Order(models.Model):
    total_price = models.FloatField()
    tax = models.FloatField()

    @property
    def final_price(self):
        return self.total_price + self.tax

12. Boolean Properties

Very useful in templates.

class Post(models.Model):
    content = models.TextField()

    @property
    def is_empty(self):
        return len(self.content.strip()) == 0

Template

{% if post.is_empty %}
    <p>No content</p>
{% endif %}

13. Formatting Methods

You can format values easily.

class Product(models.Model):
    price = models.FloatField()

    def formatted_price(self):
        return f"${self.price:.2f}"

14. Using `get_absolute_url()`

Very important built-in convention.

from django.urls import reverse

class Post(models.Model):
    slug = models.SlugField()

    def get_absolute_url(self):
        return reverse('post_detail', kwargs={'slug': self.slug})

Why it’s useful

used by Django admin
used by generic views
helps with redirects

15. Overriding `save()` Method

You can customize saving behavior.

Example

from django.utils.text import slugify

class Post(models.Model):
    title = models.CharField(max_length=200)
    slug = models.SlugField(blank=True)

    def save(self, *args, **kwargs):
        if not self.slug:
            self.slug = slugify(self.title)
        super().save(*args, **kwargs)

16. When to Use Model Methods

Use model methods when:

logic belongs to the data
you want reusable code
you want to keep views clean
you want better code organization

17. When NOT to Use Model Methods

Avoid putting:

heavy business workflows
external API calls
complex multi-model operations

For those, use:

services
utility functions
separate modules

18. Best Practices

keep methods simple and clear
use @property for computed values
always define __str__()
avoid duplicating logic in views
keep models readable
use meaningful method names

19. Common Mistakes

Forgetting `@property`

def final_price(self):

Then using:

product.final_price

⚠️ This will not work as expected.

Writing too much logic in models

Models should not become too complex.

Using methods incorrectly in templates

{{ product.final_price() }} ❌

Correct:

{{ product.final_price }} ✔️

20. Mini Project Example

E-commerce Product Model

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.FloatField()
    discount = models.FloatField(default=0)
    stock = models.IntegerField()

    @property
    def final_price(self):
        return self.price - (self.price * self.discount / 100)

    @property
    def in_stock(self):
        return self.stock > 0

    def short_name(self):
        return self.name[:20]

Template Example

<h2>{{ product.short_name }}</h2>
<p>Price: {{ product.final_price }}</p>

{% if product.in_stock %}
    <span>Available</span>
{% else %}
    <span>Out of stock</span>
{% endif %}

21. Summary

In this tutorial, you learned:

model methods add behavior to models
properties create computed attributes
@property simplifies access
__str__() defines representation
get_absolute_url() helps with routing
overriding save() customizes behavior
logic should live inside models when appropriate

Using model methods and properties makes your Django applications cleaner, more organized, and easier to maintain.

22. Mini Quiz

1. What is a model method?

A. A database field
B. A Python function inside a model
C. A template tag
D. A URL

2. What does `@property` do?

A. Creates a database field
B. Converts a method into an attribute
C. Deletes a field
D. Creates a query

3. How do you access a property?

A. obj.property()
B. obj.property
C. property(obj)
D. obj.get_property()

4. Which method defines how an object is displayed?

A. display()
B. __str__()
C. show()
D. toString()

5. What is `get_absolute_url()` used for?

A. Styling templates
B. Database queries
C. Returning a URL for an object
D. Authentication

23. What Comes Next?

Next tutorial:

Tutorial: Django Slugs and Clean URLs
You will learn how to create SEO-friendly URLs and improve your application’s structure.

Introduction

What You Will Learn

Prerequisites

1. What Are Model Methods?

2. Basic Example of a Model Method

models.py

Usage in Python

Usage in Template

3. The Special __str__() Method

4. Model Methods with Logic

Example

Usage

Template

5. What Are Model Properties?

6. Example of @property

Usage

Template

7. Method vs Property

8. Real Example: Blog Model

Usage

9. Using Model Methods in Templates

10. Model Methods with Relationships

Example

Usage

Template

11. Computed Fields Example

12. Boolean Properties

Template

13. Formatting Methods

14. Using get_absolute_url()

Why it’s useful

15. Overriding save() Method

Example

16. When to Use Model Methods

17. When NOT to Use Model Methods

18. Best Practices

19. Common Mistakes

Forgetting @property

Writing too much logic in models

Using methods incorrectly in templates

20. Mini Project Example

E-commerce Product Model

Template Example

21. Summary

22. Mini Quiz

1. What is a model method?

2. What does @property do?

3. How do you access a property?

4. Which method defines how an object is displayed?

5. What is get_absolute_url() used for?

23. What Comes Next?

`models.py`

3. The Special `str()` Method

6. Example of `@property`

14. Using `get_absolute_url()`

15. Overriding `save()` Method

Forgetting `@property`

2. What does `@property` do?

5. What is `get_absolute_url()` used for?