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 simple contact form:

forms.py
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:

views.py
from myapp.forms import ContactForm
from django.views.generic.edit import FormView

class ContactView(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:

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) simply set form_class on your view.

Σημείωση

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:

models.py
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:

views.py
from django.urls import reverse_lazy
from django.views.generic.edit import CreateView, DeleteView, UpdateView
from myapp.models import Author

class AuthorCreate(CreateView):
    model = Author
    fields = ['name']

class AuthorUpdate(UpdateView):
    model = Author
    fields = ['name']

class AuthorDelete(DeleteView):
    model = Author
    success_url = reverse_lazy('author-list')

Σημείωση

We have to use reverse_lazy() here, not just 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:

urls.py
from django.urls import path
from myapp.views import AuthorCreate, AuthorDelete, AuthorUpdate

urlpatterns = [
    # ...
    path('author/add/', AuthorCreate.as_view(), name='author-add'),
    path('author/<int:pk>/', AuthorUpdate.as_view(), name='author-update'),
    path('author/<int:pk>/delete/', AuthorDelete.as_view(), name='author-delete'),
]

Σημείωση

These views inherit SingleObjectTemplateResponseMixin which uses template_name_suffix to construct the template_name based on the model.

In this example:

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:

models.py
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:

views.py
from django.views.generic.edit import CreateView
from myapp.models import Author

class AuthorCreate(CreateView):
    model = Author
    fields = ['name']

    def form_valid(self, form):
        form.instance.created_by = self.request.user
        return super().form_valid(form)

Note that you’ll need to decorate this view using login_required(), or alternatively handle unauthorized users in the form_valid().

AJAX example

Here is a simple example showing how you might go about implementing a form that works for AJAX requests as well as “normal” form POSTs:

from django.http import JsonResponse
from django.views.generic.edit import CreateView
from myapp.models import Author

class AjaxableResponseMixin:
    """
    Mixin to add AJAX 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.is_ajax():
            return JsonResponse(form.errors, status=400)
        else:
            return response

    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.is_ajax():
            data = {
                'pk': self.object.pk,
            }
            return JsonResponse(data)
        else:
            return response

class AuthorCreate(AjaxableResponseMixin, CreateView):
    model = Author
    fields = ['name']
Built-in class-based generic views
Using mixins with class-based views
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