Function-Based Views

Views are Python functions (or classes) that receive HTTP requests and return HTTP responses. They're the heart of your application's logic.

Basic View Structure

A view function:

1. Receives an HttpRequest object
2. Does some work (query database, process data, etc.)
3. Returns an HttpResponse object

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


def index(request):
    return HttpResponse("Hello, world!")

Views with Database Queries

Let's create more useful views:

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


def index(request):
    latest_questions = Question.objects.order_by('-pub_date')[:5]
    output = ', '.join([q.question_text for q in latest_questions])
    return HttpResponse(output)


def detail(request, question_id):
    question = Question.objects.get(pk=question_id)
    return HttpResponse(f"Question: {question.question_text}")


def results(request, question_id):
    return HttpResponse(f"Results for question {question_id}")


def vote(request, question_id):
    return HttpResponse(f"Voting on question {question_id}")

URL Configuration

Map URLs to views in urls.py:

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

urlpatterns = [
    # /polls/
    path('', views.index, name='index'),
    # /polls/5/
    path('<int:question_id>/', views.detail, name='detail'),
    # /polls/5/results/
    path('<int:question_id>/results/', views.results, name='results'),
    # /polls/5/vote/
    path('<int:question_id>/vote/', views.vote, name='vote'),
]

URL Path Converters

Django provides path converters to capture URL parts:

python
# Examples
path('articles/<int:year>/', views.year_archive),
path('articles/<int:year>/<int:month>/', views.month_archive),
path('articles/<int:year>/<int:month>/<slug:slug>/', views.article_detail),

Handling Errors

What if an object doesn't exist?

python
from django.http import Http404

def detail(request, question_id):
    try:
        question = Question.objects.get(pk=question_id)
    except Question.DoesNotExist:
        raise Http404("Question does not exist")
    return HttpResponse(f"Question: {question.question_text}")

Shortcut: get_object_or_404

Django provides a helpful shortcut:

python
from django.shortcuts import get_object_or_404

def detail(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    return HttpResponse(f"Question: {question.question_text}")

Also available: get_list_or_404() for QuerySets.

Request Object

The request object contains information about the HTTP request:

python
def my_view(request):
    # HTTP method
    method = request.method  # 'GET', 'POST', etc.
    
    # GET parameters (?name=value)
    name = request.GET.get('name', 'default')
    
    # POST data
    if request.method == 'POST':
        username = request.POST.get('username')
    
    # Request path
    path = request.path  # '/polls/5/'
    
    # User (if authenticated)
    user = request.user
    
    # Is AJAX request?
    is_ajax = request.headers.get('X-Requested-With') == 'XMLHttpRequest'

Common Pitfalls

• Not handling missing objects: Using Model.objects.get() directly in views will raise a 500 error if the object does not exist. Always use get_object_or_404() instead.
• Forgetting to check request.method: Views that handle both GET and POST should check request.method to avoid processing form submissions on initial page loads.
• Returning strings instead of HttpResponse: Views must return HttpResponse objects (or subclasses). Returning a plain string will raise a ValueError.

Best Practices

• Use render() shortcut instead of manually loading templates and creating HttpResponse objects.
• Use get_object_or_404() for retrieving single objects to automatically return 404 for missing records.
• Keep views thin: Move complex business logic to model methods or service functions, not view functions.

Summary

• Views are Python functions that receive an HttpRequest and return an HttpResponse
• URL path converters (<int:pk>, <slug:slug>) capture URL segments as view arguments
• Use render() to combine a template with context data into a response
• Use get_object_or_404() to safely retrieve objects or return a 404 page
• The request object provides access to method, GET/POST data, user, and headers

from django.shortcuts import render, get_object_or_404
from .models import Question

def detail(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    return render(request, 'polls/detail.html', {'question': question})