| ============= |
| Writing views |
| ============= |
|
|
| A view function, or *view* for short, is a Python function that takes a |
| web request and returns a web response. This response can be the HTML contents |
| of a web page, or a redirect, or a 404 error, or an XML document, or an image . |
| . . or anything, really. The view itself contains whatever arbitrary logic is |
| necessary to return that response. This code can live anywhere you want, as long |
| as it's on your Python path. There's no other requirement--no "magic," so to |
| speak. For the sake of putting the code *somewhere*, the convention is to |
| put views in a file called ``views.py``, placed in your project or |
| application directory. |
|
|
| A simple view |
| ============= |
|
|
| Here's a view that returns the current date and time, as an HTML document:: |
|
|
| from django.http import HttpResponse |
| import datetime |
|
|
|
|
| def current_datetime(request): |
| now = datetime.datetime.now() |
| html = "<html><body>It is now %s.</body></html>" % now |
| return HttpResponse(html) |
|
|
| Let's step through this code one line at a time: |
|
|
| * First, we import the class :class:`~django.http.HttpResponse` from the |
| :mod:`django.http` module, along with Python's ``datetime`` library. |
|
|
| * Next, we define a function called ``current_datetime``. This is the view |
| function. Each view function takes an :class:`~django.http.HttpRequest` |
| object as its first parameter, which is typically named ``request``. |
|
|
| Note that the name of the view function doesn't matter; it doesn't have to |
| be named in a certain way in order for Django to recognize it. We're |
| calling it ``current_datetime`` here, because that name clearly indicates |
| what it does. |
|
|
| * The view returns an :class:`~django.http.HttpResponse` object that |
| contains the generated response. Each view function is responsible for |
| returning an :class:`~django.http.HttpResponse` object. (There are |
| exceptions, but we'll get to those later.) |
|
|
| .. admonition:: Django's Time Zone |
|
|
| Django includes a :setting:`TIME_ZONE` setting that defaults to |
| ``America/Chicago``. This probably isn't where you live, so you might want |
| to change it in your settings file. |
|
|
| Mapping URLs to views |
| ===================== |
|
|
| So, to recap, this view function returns an HTML page that includes the current |
| date and time. To display this view at a particular URL, you'll need to create a |
| *URLconf*; see :doc:`/topics/http/urls` for instructions. |
|
|
| Returning errors |
| ================ |
|
|
| Django provides help for returning HTTP error codes. There are subclasses of |
| :class:`~django.http.HttpResponse` for a number of common HTTP status codes |
| other than 200 (which means *"OK"*). You can find the full list of available |
| subclasses in the :ref:`request/response <ref-httpresponse-subclasses>` |
| documentation. Return an instance of one of those subclasses instead of a |
| normal :class:`~django.http.HttpResponse` in order to signify an error. For |
| example:: |
|
|
| from django.http import HttpResponse, HttpResponseNotFound |
|
|
|
|
| def my_view(request): |
| # ... |
| if foo: |
| return HttpResponseNotFound("<h1>Page not found</h1>") |
| else: |
| return HttpResponse("<h1>Page was found</h1>") |
|
|
| There isn't a specialized subclass for every possible HTTP response code, |
| since many of them aren't going to be that common. However, as documented in |
| the :class:`~django.http.HttpResponse` documentation, you can also pass the |
| HTTP status code into the constructor for :class:`~django.http.HttpResponse` |
| to create a return class for any status code you like. For example:: |
|
|
| from django.http import HttpResponse |
|
|
|
|
| def my_view(request): |
| # ... |
|
|
| # Return a "created" (201) response code. |
| return HttpResponse(status=201) |
|
|
| Because 404 errors are by far the most common HTTP error, there's an easier way |
| to handle those errors. |
|
|
| The ``Http404`` exception |
| ------------------------- |
|
|
| .. class:: django.http.Http404() |
|
|
| When you return an error such as :class:`~django.http.HttpResponseNotFound`, |
| you're responsible for defining the HTML of the resulting error page:: |
|
|
| return HttpResponseNotFound("<h1>Page not found</h1>") |
|
|
| For convenience, and because it's a good idea to have a consistent 404 error page |
| across your site, Django provides an ``Http404`` exception. If you raise |
| ``Http404`` at any point in a view function, Django will catch it and return the |
| standard error page for your application, along with an HTTP error code 404. |
|
|
| Example usage:: |
|
|
| from django.http import Http404 |
| from django.shortcuts import render |
| from polls.models import Poll |
|
|
|
|
| def detail(request, poll_id): |
| try: |
| p = Poll.objects.get(pk=poll_id) |
| except Poll.DoesNotExist: |
| raise Http404("Poll does not exist") |
| return render(request, "polls/detail.html", {"poll": p}) |
|
|
| In order to show customized HTML when Django returns a 404, you can create an |
| HTML template named ``404.html`` and place it in the top level of your |
| template tree. This template will then be served when :setting:`DEBUG` is set |
| to ``False``. |
|
|
| When :setting:`DEBUG` is ``True``, you can provide a message to ``Http404`` and |
| it will appear in the standard 404 debug template. Use these messages for |
| debugging purposes; they generally aren't suitable for use in a production 404 |
| template. |
|
|
| .. _customizing-error-views: |
|
|
| Customizing error views |
| ======================= |
|
|
| The default error views in Django should suffice for most web applications, |
| but can easily be overridden if you need any custom behavior. Specify the |
| handlers as seen below in your URLconf (setting them anywhere else will have no |
| effect). |
|
|
| The :func:`~django.views.defaults.page_not_found` view is overridden by |
| :data:`~django.conf.urls.handler404`:: |
|
|
| handler404 = "mysite.views.my_custom_page_not_found_view" |
|
|
| The :func:`~django.views.defaults.server_error` view is overridden by |
| :data:`~django.conf.urls.handler500`:: |
|
|
| handler500 = "mysite.views.my_custom_error_view" |
|
|
| The :func:`~django.views.defaults.permission_denied` view is overridden by |
| :data:`~django.conf.urls.handler403`:: |
|
|
| handler403 = "mysite.views.my_custom_permission_denied_view" |
|
|
| The :func:`~django.views.defaults.bad_request` view is overridden by |
| :data:`~django.conf.urls.handler400`:: |
|
|
| handler400 = "mysite.views.my_custom_bad_request_view" |
|
|
| .. seealso:: |
|
|
| Use the :setting:`CSRF_FAILURE_VIEW` setting to override the CSRF error |
| view. |
|
|
| Testing custom error views |
| -------------------------- |
|
|
| To test the response of a custom error handler, raise the appropriate exception |
| in a test view. For example:: |
|
|
| from django.core.exceptions import PermissionDenied |
| from django.http import HttpResponse |
| from django.test import SimpleTestCase, override_settings |
| from django.urls import path |
|
|
|
|
| def response_error_handler(request, exception=None): |
| return HttpResponse("Error handler content", status=403) |
|
|
|
|
| def permission_denied_view(request): |
| raise PermissionDenied |
|
|
|
|
| urlpatterns = [ |
| path("403/", permission_denied_view), |
| ] |
|
|
| handler403 = response_error_handler |
|
|
|
|
| # ROOT_URLCONF must specify the module that contains handler403 = ... |
| @override_settings(ROOT_URLCONF=__name__) |
| class CustomErrorHandlerTests(SimpleTestCase): |
| def test_handler_renders_template_response(self): |
| response = self.client.get("/403/") |
| # Make assertions on the response here. For example: |
| self.assertContains(response, "Error handler content", status_code=403) |
|
|
| .. _async-views: |
|
|
| Async views |
| =========== |
|
|
| As well as being synchronous functions, views can also be asynchronous |
| ("async") functions, normally defined using Python's ``async def`` syntax. |
| Django will automatically detect these and run them in an async context. |
| However, you will need to use an async server based on ASGI to get their |
| performance benefits. |
|
|
| Here's an example of an async view:: |
|
|
| import datetime |
| from django.http import HttpResponse |
|
|
|
|
| async def current_datetime(request): |
| now = datetime.datetime.now() |
| html = "<html><body>It is now %s.</body></html>" % now |
| return HttpResponse(html) |
|
|
| You can read more about Django's async support, and how to best use async |
| views, in :doc:`/topics/async`. |
|
|
