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 :ref:`Using a form in a view<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(ContactView, self).form_valid(form)
Notes:
* FormView inherits
:class:`~django.views.generic.base.TemplateResponseMixin` so
:attr:`~django.views.generic.base.TemplateResponseMixin.template_name`
can be used here.
* The default implementation for
:meth:`~django.views.generic.edit.FormMixin.form_valid` simply
redirects to the :attr:`~django.views.generic.edit.FormMixin.success_url`.
Model Forms
-----------
Generic views really shine when working with models. These generic
views will automatically create a :class:`~django.forms.ModelForm`, so long as
they can work out which model class to use:
* If the :attr:`~django.views.generic.edit.ModelFormMixin.model` attribute is
given, that model class will be used.
* If :meth:`~django.views.generic.detail.SingleObjectMixin.get_object()`
returns an object, the class of that object will be used.
* If a :attr:`~django.views.generic.detail.SingleObjectMixin.queryset` is
given, the model for that queryset will be used.
Model form views provide a
:meth:`~django.views.generic.edit.ModelFormMixin.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
:class:`~django.views.generic.edit.CreateView` or
:class:`~django.views.generic.edit.UpdateView` - they will use
:meth:`~django.db.models.Model.get_absolute_url()` on the model object if available.
If you want to use a custom :class:`~django.forms.ModelForm` (for instance to
add extra validation) simply set
:attr:`~django.views.generic.edit.FormMixin.form_class` on your view.
.. note::
When specifying a custom form class, you must still specify the model,
even though the :attr:`~django.views.generic.edit.FormMixin.form_class` may
be a :class:`~django.forms.ModelForm`.
First we need to add :meth:`~django.db.models.Model.get_absolute_url()` to our
``Author`` class:
.. code-block:: python
# models.py
from django.core.urlresolvers import reverse
from django.db import models
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 :class:`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.views.generic.edit import CreateView, UpdateView, DeleteView
from django.core.urlresolvers import reverse_lazy
from myapp.models import Author
class AuthorCreate(CreateView):
model = Author
class AuthorUpdate(UpdateView):
model = Author
class AuthorDelete(DeleteView):
model = Author
success_url = reverse_lazy('author-list')
.. note::
We have to use :func:`~django.core.urlresolvers.reverse_lazy` here, not
just ``reverse`` as the urls are not loaded when the file is imported.
Finally, we hook these new views into the URLconf::
# urls.py
from django.conf.urls import patterns, url
from myapp.views import AuthorCreate, AuthorUpdate, AuthorDelete
urlpatterns = patterns('',
# ...
url(r'author/add/$', AuthorCreate.as_view(), name='author_add'),
url(r'author/(?P<pk>\d+)/$', AuthorUpdate.as_view(), name='author_update'),
url(r'author/(?P<pk>\d+)/delete/$', AuthorDelete.as_view(), name='author_delete'),
)
.. note::
These views inherit
:class:`~django.views.generic.detail.SingleObjectTemplateResponseMixin`
which uses
:attr:`~django.views.generic.detail.SingleObjectTemplateResponseMixin.template_name_suffix`
to construct the
:attr:`~django.views.generic.base.TemplateResponseMixin.template_name`
based on the model.
In this example:
* :class:`CreateView` and :class:`UpdateView` use ``myapp/author_form.html``
* :class:`DeleteView` uses ``myapp/author_confirm_delete.html``
If you wish to have separate templates for :class:`CreateView` and
:class:`UpdateView`, you can set either
:attr:`~django.views.generic.base.TemplateResponseMixin.template_name` or
:attr:`~django.views.generic.detail.SingleObjectTemplateResponseMixin.template_name_suffix`
on your view class.
Models and request.user
-----------------------
To track the user that created an object using a :class:`CreateView`,
you can use a custom :class:`~django.forms.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)
# ...
Create a custom :class:`~django.forms.ModelForm` in order to exclude the
``created_by`` field and prevent the user from editing it:
.. code-block:: python
# forms.py
from django import forms
from myapp.models import Author
class AuthorForm(forms.ModelForm):
class Meta:
model = Author
exclude = ('created_by',)
In the view, use the custom
:attr:`~django.views.generic.edit.FormMixin.form_class` and override
:meth:`~django.views.generic.edit.ModelFormMixin.form_valid()` to add the
user::
# views.py
from django.views.generic.edit import CreateView
from myapp.models import Author
from myapp.forms import AuthorForm
class AuthorCreate(CreateView):
form_class = AuthorForm
model = Author
def form_valid(self, form):
form.instance.created_by = self.request.user
return super(AuthorCreate, self).form_valid(form)
Note that you'll need to :ref:`decorate this
view<decorating-class-based-views>` using
:func:`~django.contrib.auth.decorators.login_required`, or
alternatively handle unauthorized users in the
:meth:`~django.views.generic.edit.ModelFormMixin.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::
import json
from django.http import HttpResponse
from django.views.generic.edit import CreateView
class AjaxableResponseMixin(object):
"""
Mixin to add AJAX support to a form.
Must be used with an object-based FormView (e.g. CreateView)
"""
def render_to_json_response(self, context, **response_kwargs):
data = json.dumps(context)
response_kwargs['content_type'] = 'application/json'
return HttpResponse(data, **response_kwargs)
def form_invalid(self, form):
response = super(AjaxableResponseMixin, self).form_invalid(form)
if self.request.is_ajax():
return self.render_to_json_response(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(AjaxableResponseMixin, self).form_valid(form)
if self.request.is_ajax():
data = {
'pk': self.object.pk,
}
return self.render_to_json_response(data)
else:
return response
class AuthorCreate(AjaxableResponseMixin, CreateView):
model = Author
