Form handling with class-based views¶
Form processing generally has 3 paths:
- Initial GET (blank or prepopulated form)
- POST with invalid data (typically redisplay form with errors)
- POST with valid data (process the data and typically redirect)
Implementing this yourself often results in a lot of repeated boilerplate code (see Using a form in a view). To help avoid this, Django provides a collection of generic class-based views for form processing.
Basic forms¶
Given a contact form:
from django import forms
class ContactForm(forms.Form):
name = forms.CharField()
message = forms.CharField(widget=forms.Textarea)
def send_email(self):
# send email using the self.cleaned_data dictionary
pass
The view can be constructed using a FormView
:
from myapp.forms import ContactForm
from django.views.generic.edit import FormView
class ContactFormView(FormView):
template_name = 'contact.html'
form_class = ContactForm
success_url = '/thanks/'
def form_valid(self, form):
# This method is called when valid form data has been POSTed.
# It should return an HttpResponse.
form.send_email()
return super().form_valid(form)
Notes:
- FormView inherits
TemplateResponseMixin
sotemplate_name
can be used here. - The default implementation for
form_valid()
simply redirects to thesuccess_url
.
Model forms¶
Generic views really shine when working with models. These generic
views will automatically create a ModelForm
, so long as
they can work out which model class to use:
- If the
model
attribute is given, that model class will be used. - If
get_object()
returns an object, the class of that object will be used. - If a
queryset
is given, the model for that queryset will be used.
Model form views provide a
form_valid()
implementation
that saves the model automatically. You can override this if you have any
special requirements; see below for examples.
You don’t even need to provide a success_url
for
CreateView
or
UpdateView
- they will use
get_absolute_url()
on the model object if available.
If you want to use a custom ModelForm
(for instance to
add extra validation), set
form_class
on your view.
Note
When specifying a custom form class, you must still specify the model,
even though the form_class
may
be a ModelForm
.
First we need to add get_absolute_url()
to our
Author
class:
from django.db import models
from django.urls import reverse
class Author(models.Model):
name = models.CharField(max_length=200)
def get_absolute_url(self):
return reverse('author-detail', kwargs={'pk': self.pk})
Then we can use CreateView
and friends to do the actual
work. Notice how we’re just configuring the generic class-based views
here; we don’t have to write any logic ourselves:
from django.urls import reverse_lazy
from django.views.generic.edit import CreateView, DeleteView, UpdateView
from myapp.models import Author
class AuthorCreateView(CreateView):
model = Author
fields = ['name']
class AuthorUpdateView(UpdateView):
model = Author
fields = ['name']
class AuthorDeleteView(DeleteView):
model = Author
success_url = reverse_lazy('author-list')
Note
We have to use reverse_lazy()
instead of
reverse()
, as the urls are not loaded when the file is imported.
The fields
attribute works the same way as the fields
attribute on the
inner Meta
class on ModelForm
. Unless you define the
form class in another way, the attribute is required and the view will raise
an ImproperlyConfigured
exception if it’s not.
If you specify both the fields
and form_class
attributes, an
ImproperlyConfigured
exception will be raised.
Finally, we hook these new views into the URLconf:
from django.urls import path
from myapp.views import AuthorCreateView, AuthorDeleteView, AuthorUpdateView
urlpatterns = [
# ...
path('author/add/', AuthorCreateView.as_view(), name='author-add'),
path('author/<int:pk>/', AuthorUpdateView.as_view(), name='author-update'),
path('author/<int:pk>/delete/', AuthorDeleteView.as_view(), name='author-delete'),
]
Note
These views inherit
SingleObjectTemplateResponseMixin
which uses
template_name_suffix
to construct the
template_name
based on the model.
In this example:
CreateView
andUpdateView
usemyapp/author_form.html
DeleteView
usesmyapp/author_confirm_delete.html
If you wish to have separate templates for CreateView
and
UpdateView
, you can set either
template_name
or
template_name_suffix
on your view class.
Models and request.user
¶
To track the user that created an object using a CreateView
,
you can use a custom ModelForm
to do this. First, add
the foreign key relation to the model:
from django.contrib.auth.models import User
from django.db import models
class Author(models.Model):
name = models.CharField(max_length=200)
created_by = models.ForeignKey(User, on_delete=models.CASCADE)
# ...
In the view, ensure that you don’t include created_by
in the list of fields
to edit, and override
form_valid()
to add the user:
from django.contrib.auth.mixins import LoginRequiredMixin
from django.views.generic.edit import CreateView
from myapp.models import Author
class AuthorCreateView(LoginRequiredMixin, CreateView):
model = Author
fields = ['name']
def form_valid(self, form):
form.instance.created_by = self.request.user
return super().form_valid(form)
LoginRequiredMixin
prevents users who
aren’t logged in from accessing the form. If you omit that, you’ll need to
handle unauthorized users in form_valid()
.
Content negotiation example¶
Here is an example showing how you might go about implementing a form that works with an API-based workflow as well as ‘normal’ form POSTs:
from django.http import JsonResponse
from django.views.generic.edit import CreateView
from myapp.models import Author
class JsonableResponseMixin:
"""
Mixin to add JSON support to a form.
Must be used with an object-based FormView (e.g. CreateView)
"""
def form_invalid(self, form):
response = super().form_invalid(form)
if self.request.accepts('text/html'):
return response
else:
return JsonResponse(form.errors, status=400)
def form_valid(self, form):
# We make sure to call the parent's form_valid() method because
# it might do some processing (in the case of CreateView, it will
# call form.save() for example).
response = super().form_valid(form)
if self.request.accepts('text/html'):
return response
else:
data = {
'pk': self.object.pk,
}
return JsonResponse(data)
class AuthorCreateView(JsonableResponseMixin, CreateView):
model = Author
fields = ['name']