Introduction to Class-Based Views

Class-Based Views (CBVs) are an alternative to function-based views that use Python classes. They provide inheritance, mixins, and built-in patterns for common tasks.

Why Class-Based Views?

Basic Class-Based View

A class-based view defines separate methods for each HTTP method. Django's View base class routes requests to the appropriate method automatically.

python
# polls/views.py
from django.http import HttpResponse
from django.views import View


class HomeView(View):
    def get(self, request):
        return HttpResponse("Hello from GET!")
    
    def post(self, request):
        return HttpResponse("Hello from POST!")

URL Configuration

Class-based views must be converted to callable functions using .as_view() before they can be used in URL patterns.

python
# polls/urls.py
from django.urls import path
from .views import HomeView

urlpatterns = [
    path('', HomeView.as_view(), name='home'),
]

Use .as_view() to convert the class to a view function.

TemplateView

Render a template without custom logic:

python
from django.views.generic import TemplateView


class AboutView(TemplateView):
    template_name = 'about.html'
    
    # Optional: add context
    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context['page_title'] = 'About Us'
        return context

Or directly in URLs:

python
urlpatterns = [
    path('about/', TemplateView.as_view(template_name='about.html'), name='about'),
]

ListView

Display a list of objects:

python
from django.views.generic import ListView
from .models import Question


class QuestionListView(ListView):
    model = Question
    template_name = 'polls/question_list.html'  # Default: polls/question_list.html
    context_object_name = 'questions'            # Default: object_list
    ordering = ['-pub_date']
    paginate_by = 10  # Enable pagination
    
    def get_queryset(self):
        """Custom filtering."""
        return Question.objects.filter(is_active=True)

html
<!-- polls/templates/polls/question_list.html -->
<h1>Questions</h1>
<ul>
{% for question in questions %}
    <li>{{ question.question_text }}</li>
{% empty %}
    <li>No questions available.</li>
{% endfor %}
</ul>

<!-- Pagination -->
{% if is_paginated %}
<nav>
    {% if page_obj.has_previous %}
        <a href="?page={{ page_obj.previous_page_number }}">Previous</a>
    {% endif %}
    
    Page {{ page_obj.number }} of {{ page_obj.paginator.num_pages }}
    
    {% if page_obj.has_next %}
        <a href="?page={{ page_obj.next_page_number }}">Next</a>
    {% endif %}
</nav>
{% endif %}

DetailView

Display a single object:

python
from django.views.generic import DetailView


class QuestionDetailView(DetailView):
    model = Question
    template_name = 'polls/question_detail.html'
    context_object_name = 'question'

python
# urls.py
urlpatterns = [
    path('<int:pk>/', QuestionDetailView.as_view(), name='detail'),
    # Or use slug
    path('<slug:slug>/', QuestionDetailView.as_view(), name='detail'),
]

html
<!-- polls/templates/polls/question_detail.html -->
<h1>{{ question.question_text }}</h1>
<p>Published: {{ question.pub_date }}</p>

<h2>Choices:</h2>
<ul>
{% for choice in question.choice_set.all %}
    <li>{{ choice.choice_text }} - {{ choice.votes }} votes</li>
{% endfor %}
</ul>

Common Pitfalls

• Forgetting .as_view() in URL patterns: Class-based views must be called with .as_view() in urlpatterns. Without it, Django raises a TypeError.
• Confusing template_name defaults: If you don't set template_name, Django expects app/model_list.html for ListView and app/model_detail.html for DetailView.
• Not calling super() in overridden methods: When overriding get_context_data() or get_queryset(), always call super() first to preserve the default behavior.

Best Practices

• Set context_object_name for readable template variable names instead of the default object_list.
• Override get_queryset() for custom filtering instead of hardcoding queries.
• Use paginate_by on ListViews to prevent loading too many objects at once.

Summary

• Class-based views use Python classes with methods for each HTTP method (get(), post())
• TemplateView, ListView, and DetailView are the most common generic display views
• Use .as_view() in URL patterns to convert a class into a callable view function
• Override get_queryset() for custom filtering and get_context_data() for extra context
• CBVs support inheritance and mixins for code reuse across views

from django.views.generic import ListView
from .models import Question

class QuestionListView(ListView):
    model = Question
    template_name = 'polls/question_list.html'
    context_object_name = 'questions'
    ordering = ['-pub_date']
    paginate_by = 10

# urls.py
path('', QuestionListView.as_view(), name='index')