Custom permissions in Django - Mini Project: Build & Apply

Custom Permissions in Django

📖 Scenario: You are building a Django web app where only certain users can edit articles. You want to create a custom permission to control who can update articles.

🎯 Goal: Create a custom permission called can_edit_article and apply it to an Article model. Then check this permission in a view to allow or deny editing.

📋 What You'll Learn

Create an Article model with a title and content fields

Add a custom permission can_edit_article to the Article model

Create a variable user_can_edit that checks if a user has the can_edit_article permission

Use the permission check in a view function to allow editing only if user_can_edit is True

💡 Why This Matters

🌍 Real World

Custom permissions help control who can do what in your web app, like letting only editors update articles.

💼 Career

Understanding custom permissions is important for building secure Django apps and is a common task for backend developers.

1

Create the Article model

Create a Django model called Article with two fields: title as a CharField with max length 100, and content as a TextField.

Django

# Your code here
from django.db import models

# Define the Article model below

Hint

Use models.CharField for short text and models.TextField for longer text.

2

Add a custom permission to the Article model

Add a Meta class inside the Article model. Inside Meta, add a permissions list with a tuple ("can_edit_article", "Can edit article").

Django

from django.db import models

class Article(models.Model):
    title = models.CharField(max_length=100)
    content = models.TextField()

    # Add Meta class with custom permissions below
    

Hint

The permissions attribute is a list of tuples inside the Meta class.

3

Check the custom permission in a variable

Create a variable called user_can_edit that checks if a user has the permission "app_label.can_edit_article". Use user.has_perm("app_label.can_edit_article"). Replace app_label with the app name blog.

Django

from django.db import models

class Article(models.Model):
    title = models.CharField(max_length=100)
    content = models.TextField()

    class Meta:
        permissions = [("can_edit_article", "Can edit article")]

# Check if user has permission below
user_can_edit = None  # Your code here

Hint

Use the exact string "blog.can_edit_article" inside has_perm().

4

Use the permission check in a view

In a Django view function called edit_article, use an if statement to check user_can_edit. If True, return HttpResponse("Edit allowed"). Otherwise, return HttpResponseForbidden(). Import HttpResponse and HttpResponseForbidden from django.http.

Django

from django.db import models
from django.http import HttpResponse, HttpResponseForbidden

class Article(models.Model):
    title = models.CharField(max_length=100)
    content = models.TextField()

    class Meta:
        permissions = [("can_edit_article", "Can edit article")]

user_can_edit = user.has_perm("blog.can_edit_article")

# Define the edit_article view below

Hint

Use if user_can_edit: to check permission and return the correct response.

Practice

1. What is the main purpose of creating a custom permission in Django?

easy

A. To control user access based on specific rules you define

B. To change the database schema automatically

C. To speed up the Django server response time

D. To create new database tables for users

Solution

1. Step 1: Understand what permissions do in Django

   Permissions control what users can or cannot do in the app.

2. Step 2: Identify the role of custom permissions

   Custom permissions let you define your own rules for user access beyond default ones.

3. Final Answer:

   To control user access based on specific rules you define -> Option A

4. Quick Check:

   Custom permissions = control user access [OK]

Hint: Custom permissions control access rules you create [OK]

Common Mistakes:

• Thinking permissions change database structure
• Confusing permissions with performance settings
• Believing permissions create new tables

2. Which method must you override when creating a custom permission class in Django REST Framework?

easy

A. save

B. get_queryset

C. has_permission

D. dispatch

Solution

1. Step 1: Recall the BasePermission class methods

   The main method to check access is has_permission.

2. Step 2: Confirm which method controls permission checks

   has_permission returns True or False to allow or deny access.

3. Final Answer:

   has_permission -> Option C

4. Quick Check:

   Permission check method = has_permission [OK]

Hint: Override has_permission to define access rules [OK]

Common Mistakes:

• Using get_queryset which filters data, not permissions
• Confusing save method with permission checks
• Using dispatch which is for request handling

3. Given this custom permission class, what will be the result if a user is not authenticated?

from rest_framework.permissions import BasePermission

class IsAuthenticatedCustom(BasePermission):
    def has_permission(self, request, view):
        return request.user and request.user.is_authenticated

medium

A. Code raises an error due to missing return

B. Access is denied because user is not authenticated

C. Access is granted regardless of authentication

D. Access is granted only if user is staff

Solution

1. Step 1: Analyze the has_permission method logic

   It returns True only if request.user exists and is authenticated.

2. Step 2: Consider the case when user is not authenticated

   Then request.user.is_authenticated is False, so method returns False denying access.

3. Final Answer:

   Access is denied because user is not authenticated -> Option B

4. Quick Check:

   Unauthenticated user = access denied [OK]

Hint: Check if user.is_authenticated is True to allow access [OK]

Common Mistakes:

• Assuming access is granted without authentication
• Thinking code raises error due to return statement
• Confusing staff status with authentication

4. Identify the error in this custom permission class:

from rest_framework.permissions import BasePermission

class IsOwnerPermission(BasePermission):
    def has_permission(self, request, view):
        return request.user == view.get_object().owner

medium

A. Missing import for request module

B. No return statement in has_permission

C. Incorrect comparison operator used

D. Using has_permission instead of has_object_permission for object check

Solution

1. Step 1: Understand permission methods roles

   has_permission checks general access; has_object_permission checks per object.

2. Step 2: Identify misuse of has_permission for object ownership

   Comparing user to object owner requires has_object_permission, not has_permission.

3. Final Answer:

   Using has_permission instead of has_object_permission for object check -> Option D

4. Quick Check:

   Object checks need has_object_permission [OK]

Hint: Use has_object_permission for per-object access checks [OK]

Common Mistakes:

• Confusing has_permission with has_object_permission
• Assuming import errors cause this issue
• Thinking comparison operator is wrong

5. You want to create a custom permission that allows access only if the user is authenticated and the HTTP method is safe (GET, HEAD, OPTIONS). Which is the correct implementation?

hard

A. class SafeAndAuthenticated(BasePermission):
def has_permission(self, request, view):
return request.user.is_authenticated and request.method in ['GET', 'HEAD', 'OPTIONS']

B. class SafeAndAuthenticated(BasePermission):
def has_permission(self, request, view):
return request.user.is_authenticated or request.method in ['GET', 'HEAD', 'OPTIONS']

C. class SafeAndAuthenticated(BasePermission):
def has_permission(self, request, view):
return not request.user.is_authenticated and request.method in ['GET', 'HEAD', 'OPTIONS']

D. class SafeAndAuthenticated(BasePermission):
def has_permission(self, request, view):
return request.user.is_authenticated and request.method not in ['GET', 'HEAD', 'OPTIONS']

Solution

1. Step 1: Understand the requirement

   User must be authenticated AND method must be safe (GET, HEAD, OPTIONS).

2. Step 2: Analyze each option's logic

   class SafeAndAuthenticated(BasePermission): def has_permission(self, request, view): return request.user.is_authenticated and request.method in ['GET', 'HEAD', 'OPTIONS'] uses AND with correct method list; others use OR, NOT, or wrong method checks.

3. Final Answer:

   class SafeAndAuthenticated(BasePermission): def has_permission(self, request, view): return request.user.is_authenticated and request.method in ['GET', 'HEAD', 'OPTIONS'] -> Option A

4. Quick Check:

   Use AND for combined conditions [OK]

Hint: Use AND to combine authentication and method checks [OK]

Common Mistakes:

• Using OR instead of AND allowing wrong access
• Checking for methods incorrectly with NOT
• Allowing unauthenticated users by mistake