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
        fields = ['name']

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

    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.

.. versionchanged:: 1.6

In Django 1.6, the ``fields`` attribute was added, which works the same way as
the ``fields`` attribute on the inner ``Meta`` class on
:class:`~django.forms.ModelForm`.

Omitting the fields attribute will work as previously, but is deprecated and
this attribute will be required from 1.8 (unless you define the form class in
another way).


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 import User
    from django.db import models

    class Author(models.Model):
        name = models.CharField(max_length=200)
        created_by = models.ForeignKey(User)

        # ...

In the view, ensure that you don't include ``created_by`` in the list of fields
to edit, 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

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

        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
    from myapp.models import Author

    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
        fields = ['name']
