Pagination (PageNumber, Cursor, Limit/Offset) in Django - Mini Project: Build & Apply

Pagination with Django REST Framework

📖 Scenario: You are building a simple API for a bookstore. The API should return a list of books, but since there could be many books, you want to show only a few books per page. This is called pagination.We will use Django REST Framework's built-in pagination to split the list of books into pages.

🎯 Goal: Create a Django REST Framework API view that returns a paginated list of books using PageNumberPagination. You will set up the data, configure pagination, apply it in the view, and complete the setup to see paginated results.

📋 What You'll Learn

Create a list of book dictionaries with exact titles and authors

Set a pagination page size variable

Use Django REST Framework's PageNumberPagination in the API view

Complete the API view to return paginated book data

💡 Why This Matters

🌍 Real World

APIs often return large lists of data. Pagination helps split data into pages so users can load and see data easily without waiting for everything at once.

💼 Career

Backend developers frequently implement pagination in APIs to improve performance and user experience. Knowing Django REST Framework pagination is a valuable skill.

1

DATA SETUP: Create a list of books

Create a list called books with these exact dictionaries: {'title': 'Book A', 'author': 'Author 1'}, {'title': 'Book B', 'author': 'Author 2'}, and {'title': 'Book C', 'author': 'Author 3'}.

Django

# Your code here

Hint

Use a list with three dictionaries exactly as shown.

2

CONFIGURATION: Set pagination page size

Create a variable called PAGE_SIZE and set it to 2 to limit books per page.

Django

books = [
    {'title': 'Book A', 'author': 'Author 1'},
    {'title': 'Book B', 'author': 'Author 2'},
    {'title': 'Book C', 'author': 'Author 3'}
]
# Your code here

Hint

Just create a variable named PAGE_SIZE and assign 2.

3

CORE LOGIC: Use PageNumberPagination in API view

Import PageNumberPagination from rest_framework.pagination. Create a class BookPagination that inherits from PageNumberPagination and set its page_size to PAGE_SIZE. Then create a function book_list that takes request, uses BookPagination to paginate books, and returns the paginated data as a response.

Django

books = [
    {'title': 'Book A', 'author': 'Author 1'},
    {'title': 'Book B', 'author': 'Author 2'},
    {'title': 'Book C', 'author': 'Author 3'}
]

PAGE_SIZE = 2

# Your code here

Hint

Use the Django REST Framework pagination classes and methods exactly as shown.

4

COMPLETION: Add URL pattern for the API view

Import path from django.urls. Create a list called urlpatterns with one path entry: the URL 'books/' mapped to the book_list view.

Django

from rest_framework.pagination import PageNumberPagination
from rest_framework.response import Response

books = [
    {'title': 'Book A', 'author': 'Author 1'},
    {'title': 'Book B', 'author': 'Author 2'},
    {'title': 'Book C', 'author': 'Author 3'}
]

PAGE_SIZE = 2

class BookPagination(PageNumberPagination):
    page_size = PAGE_SIZE


def book_list(request):
    paginator = BookPagination()
    page = paginator.paginate_queryset(books, request)
    return paginator.get_paginated_response(page)

# Your code here

Hint

Define urlpatterns with path 'books/' pointing to book_list.

Practice

1. Which Django REST Framework pagination style uses a page number to fetch specific pages of data?

easy

A. PageNumberPagination

B. CursorPagination

C. LimitOffsetPagination

D. OffsetPagination

Solution

1. Step 1: Understand pagination styles

   PageNumberPagination uses page numbers like 1, 2, 3 to get data pages.

2. Step 2: Match style to description

   CursorPagination uses a cursor token, LimitOffsetPagination uses limit and offset numbers, so they don't use page numbers.

3. Final Answer:

   PageNumberPagination -> Option A

4. Quick Check:

   Page number style = PageNumberPagination [OK]

Hint: PageNumberPagination uses simple page numbers like 1, 2, 3 [OK]

Common Mistakes:

• Confusing CursorPagination with page numbers
• Thinking LimitOffsetPagination uses page numbers
• Assuming OffsetPagination is a valid DRF style

2. Which of the following is the correct way to set LimitOffsetPagination in Django REST Framework settings?

easy

A. "DEFAULT_PAGINATION_CLASS": "rest_framework.pagination.OffsetPagination"

B. "DEFAULT_PAGINATION_CLASS": "rest_framework.pagination.PageNumberPagination"

C. "DEFAULT_PAGINATION_CLASS": "rest_framework.pagination.LimitOffsetPagination"

D. "DEFAULT_PAGINATION_CLASS": "rest_framework.pagination.CursorPagination"

Solution

1. Step 1: Identify correct class path

   LimitOffsetPagination is located at rest_framework.pagination.LimitOffsetPagination.

2. Step 2: Verify syntax for settings

   The setting key is DEFAULT_PAGINATION_CLASS and the value is the full class path as a string.

3. Final Answer:

   "DEFAULT_PAGINATION_CLASS": "rest_framework.pagination.LimitOffsetPagination" -> Option C

4. Quick Check:

   Correct class path and setting key = "DEFAULT_PAGINATION_CLASS": "rest_framework.pagination.LimitOffsetPagination" [OK]

Hint: Use full class path string for pagination in settings [OK]

Common Mistakes:

• Using OffsetPagination which does not exist
• Missing quotes around class path string
• Mixing pagination class names

3. Given this code snippet using CursorPagination, what will be the value of the next cursor if the current cursor is 'abc123' and page size is 2?

class MyCursorPagination(CursorPagination):
    page_size = 2

paginator = MyCursorPagination()
next_cursor = paginator.get_next_link()

medium

A. A tuple with offset and limit values

B. An integer representing the next page number

C. None, because get_next_link() returns nothing

D. A URL containing a cursor parameter with a new encoded cursor

Solution

1. Step 1: Understand CursorPagination behavior

   CursorPagination returns URLs with encoded cursor tokens for next pages, not page numbers or tuples.

2. Step 2: Analyze get_next_link() output

   get_next_link() returns a URL string containing the next cursor parameter for pagination.

3. Final Answer:

   A URL containing a cursor parameter with a new encoded cursor -> Option D

4. Quick Check:

   CursorPagination next link = URL with cursor [OK]

Hint: CursorPagination returns URLs with cursor tokens, not numbers [OK]

Common Mistakes:

• Expecting page numbers from CursorPagination
• Thinking get_next_link() returns None
• Confusing limit/offset with cursor

4. You have this Django REST Framework view using LimitOffsetPagination but it raises an error:

class MyLimitOffsetPagination(LimitOffsetPagination):
    default_limit = '10'

class MyView(ListAPIView):
    pagination_class = MyLimitOffsetPagination
    queryset = MyModel.objects.all()
    serializer_class = MySerializer

What is the likely cause of the error?

medium

A. pagination_class should be a string path, not a class

B. default_limit should be an integer, not a string

C. ListAPIView does not support pagination

D. queryset must be a list, not a QuerySet

Solution

1. Step 1: Check default_limit type

   default_limit must be an integer, but it is set as a string '10', causing a type error.

2. Step 2: Verify other parts

   pagination_class can be a class, ListAPIView supports pagination, queryset can be a QuerySet.

3. Final Answer:

   default_limit should be an integer, not a string -> Option B

4. Quick Check:

   default_limit type error = default_limit should be an integer, not a string [OK]

Hint: default_limit must be int, not quoted string [OK]

Common Mistakes:

• Setting default_limit as string instead of int
• Thinking pagination_class must be string path
• Assuming ListAPIView disables pagination

5. You want to implement pagination for a large dataset where new items are frequently added. Which pagination style is best to avoid duplicate or missing items when users navigate pages?

hard

A. CursorPagination

B. PageNumberPagination

C. LimitOffsetPagination

D. No pagination

Solution

1. Step 1: Understand pagination challenges with dynamic data

   PageNumber and LimitOffset can cause duplicates or missing items if data changes between requests.

2. Step 2: Identify pagination style that handles dynamic data well

   CursorPagination uses a stable cursor based on item order, preventing duplicates or skips when data changes.

3. Final Answer:

   CursorPagination -> Option A

4. Quick Check:

   Dynamic data needs CursorPagination [OK]

Hint: Use CursorPagination for changing data to avoid duplicates [OK]

Common Mistakes:

• Choosing PageNumberPagination for dynamic data
• Thinking LimitOffsetPagination handles data changes well
• Ignoring pagination for large datasets