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329 lines
11 KiB
Plaintext
329 lines
11 KiB
Plaintext
====================================
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Form handling with class-based views
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====================================
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Form processing generally has 3 paths:
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* Initial GET (blank or prepopulated form)
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* POST with invalid data (typically redisplay form with errors)
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* POST with valid data (process the data and typically redirect)
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Implementing this yourself often results in a lot of repeated boilerplate code
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(see :ref:`Using a form in a view<using-a-form-in-a-view>`). To help avoid
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this, Django provides a collection of generic class-based views for form
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processing.
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Basic forms
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===========
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Given a contact form:
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.. code-block:: python
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:caption: ``forms.py``
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from django import forms
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class ContactForm(forms.Form):
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name = forms.CharField()
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message = forms.CharField(widget=forms.Textarea)
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def send_email(self):
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# send email using the self.cleaned_data dictionary
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pass
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The view can be constructed using a ``FormView``:
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.. code-block:: python
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:caption: ``views.py``
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from myapp.forms import ContactForm
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from django.views.generic.edit import FormView
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class ContactFormView(FormView):
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template_name = "contact.html"
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form_class = ContactForm
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success_url = "/thanks/"
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def form_valid(self, form):
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# This method is called when valid form data has been POSTed.
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# It should return an HttpResponse.
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form.send_email()
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return super().form_valid(form)
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Notes:
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* FormView inherits
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:class:`~django.views.generic.base.TemplateResponseMixin` so
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:attr:`~django.views.generic.base.TemplateResponseMixin.template_name`
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can be used here.
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* The default implementation for
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:meth:`~django.views.generic.edit.FormMixin.form_valid` simply
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redirects to the :attr:`~django.views.generic.edit.FormMixin.success_url`.
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Model forms
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===========
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Generic views really shine when working with models. These generic
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views will automatically create a :class:`~django.forms.ModelForm`, so long as
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they can work out which model class to use:
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* If the :attr:`~django.views.generic.edit.ModelFormMixin.model` attribute is
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given, that model class will be used.
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* If :meth:`~django.views.generic.detail.SingleObjectMixin.get_object()`
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returns an object, the class of that object will be used.
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* If a :attr:`~django.views.generic.detail.SingleObjectMixin.queryset` is
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given, the model for that queryset will be used.
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Model form views provide a
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:meth:`~django.views.generic.edit.ModelFormMixin.form_valid()` implementation
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that saves the model automatically. You can override this if you have any
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special requirements; see below for examples.
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You don't even need to provide a ``success_url`` for
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:class:`~django.views.generic.edit.CreateView` or
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:class:`~django.views.generic.edit.UpdateView` - they will use
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:meth:`~django.db.models.Model.get_absolute_url()` on the model object if available.
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If you want to use a custom :class:`~django.forms.ModelForm` (for instance to
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add extra validation), set
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:attr:`~django.views.generic.edit.FormMixin.form_class` on your view.
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.. note::
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When specifying a custom form class, you must still specify the model,
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even though the :attr:`~django.views.generic.edit.FormMixin.form_class` may
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be a :class:`~django.forms.ModelForm`.
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First we need to add :meth:`~django.db.models.Model.get_absolute_url()` to our
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``Author`` class:
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.. code-block:: python
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:caption: ``models.py``
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from django.db import models
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from django.urls import reverse
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class Author(models.Model):
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name = models.CharField(max_length=200)
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def get_absolute_url(self):
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return reverse("author-detail", kwargs={"pk": self.pk})
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Then we can use :class:`CreateView` and friends to do the actual
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work. Notice how we're just configuring the generic class-based views
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here; we don't have to write any logic ourselves:
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.. code-block:: python
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:caption: ``views.py``
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from django.urls import reverse_lazy
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from django.views.generic.edit import CreateView, DeleteView, UpdateView
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from myapp.models import Author
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class AuthorCreateView(CreateView):
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model = Author
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fields = ["name"]
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class AuthorUpdateView(UpdateView):
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model = Author
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fields = ["name"]
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class AuthorDeleteView(DeleteView):
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model = Author
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success_url = reverse_lazy("author-list")
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.. note::
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We have to use :func:`~django.urls.reverse_lazy` instead of
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``reverse()``, as the urls are not loaded when the file is imported.
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The ``fields`` attribute works the same way as the ``fields`` attribute on the
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inner ``Meta`` class on :class:`~django.forms.ModelForm`. Unless you define the
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form class in another way, the attribute is required and the view will raise
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an :exc:`~django.core.exceptions.ImproperlyConfigured` exception if it's not.
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If you specify both the :attr:`~django.views.generic.edit.ModelFormMixin.fields`
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and :attr:`~django.views.generic.edit.FormMixin.form_class` attributes, an
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:exc:`~django.core.exceptions.ImproperlyConfigured` exception will be raised.
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Finally, we hook these new views into the URLconf:
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.. code-block:: python
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:caption: ``urls.py``
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from django.urls import path
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from myapp.views import AuthorCreateView, AuthorDeleteView, AuthorUpdateView
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urlpatterns = [
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# ...
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path("author/add/", AuthorCreateView.as_view(), name="author-add"),
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path("author/<int:pk>/", AuthorUpdateView.as_view(), name="author-update"),
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path("author/<int:pk>/delete/", AuthorDeleteView.as_view(), name="author-delete"),
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]
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.. note::
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These views inherit
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:class:`~django.views.generic.detail.SingleObjectTemplateResponseMixin`
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which uses
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:attr:`~django.views.generic.detail.SingleObjectTemplateResponseMixin.template_name_suffix`
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to construct the
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:attr:`~django.views.generic.base.TemplateResponseMixin.template_name`
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based on the model.
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In this example:
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* :class:`CreateView` and :class:`UpdateView` use ``myapp/author_form.html``
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* :class:`DeleteView` uses ``myapp/author_confirm_delete.html``
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If you wish to have separate templates for :class:`CreateView` and
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:class:`UpdateView`, you can set either
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:attr:`~django.views.generic.base.TemplateResponseMixin.template_name` or
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:attr:`~django.views.generic.detail.SingleObjectTemplateResponseMixin.template_name_suffix`
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on your view class.
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Models and ``request.user``
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===========================
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To track the user that created an object using a :class:`CreateView`,
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you can use a custom :class:`~django.forms.ModelForm` to do this. First, add
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the foreign key relation to the model:
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.. code-block:: python
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:caption: ``models.py``
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from django.contrib.auth.models import User
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from django.db import models
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class Author(models.Model):
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name = models.CharField(max_length=200)
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created_by = models.ForeignKey(User, on_delete=models.CASCADE)
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# ...
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In the view, ensure that you don't include ``created_by`` in the list of fields
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to edit, and override
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:meth:`~django.views.generic.edit.ModelFormMixin.form_valid()` to add the user:
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.. code-block:: python
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:caption: ``views.py``
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from django.contrib.auth.mixins import LoginRequiredMixin
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from django.views.generic.edit import CreateView
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from myapp.models import Author
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class AuthorCreateView(LoginRequiredMixin, CreateView):
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model = Author
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fields = ["name"]
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def form_valid(self, form):
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form.instance.created_by = self.request.user
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return super().form_valid(form)
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:class:`~django.contrib.auth.mixins.LoginRequiredMixin` prevents users who
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aren't logged in from accessing the form. If you omit that, you'll need to
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handle unauthorized users in :meth:`~.ModelFormMixin.form_valid()`.
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.. _content-negotiation-example:
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Content negotiation example
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===========================
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Here is an example showing how you might go about implementing a form that
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works with an API-based workflow as well as 'normal' form POSTs::
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from django.http import JsonResponse
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from django.views.generic.edit import CreateView
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from myapp.models import Author
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class JsonableResponseMixin:
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"""
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Mixin to add JSON support to a form.
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Must be used with an object-based FormView (e.g. CreateView)
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"""
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def form_invalid(self, form):
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response = super().form_invalid(form)
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if self.request.accepts("text/html"):
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return response
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else:
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return JsonResponse(form.errors, status=400)
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def form_valid(self, form):
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# We make sure to call the parent's form_valid() method because
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# it might do some processing (in the case of CreateView, it will
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# call form.save() for example).
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response = super().form_valid(form)
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if self.request.accepts("text/html"):
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return response
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else:
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data = {
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"pk": self.object.pk,
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}
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return JsonResponse(data)
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class AuthorCreateView(JsonableResponseMixin, CreateView):
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model = Author
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fields = ["name"]
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The above example assumes that if the client supports ``text/html``, that they
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would prefer it. However, this may not always be true. When requesting a
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``.css`` file, many browsers will send the header
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``Accept: text/css,*/*;q=0.1``, indicating that they would prefer CSS, but
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anything else is fine. This means ``request.accepts("text/html")`` will be
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``True``.
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To determine the correct format, taking into consideration the client's
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preference, use :func:`django.http.HttpRequest.get_preferred_type`::
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class JsonableResponseMixin:
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"""
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Mixin to add JSON support to a form.
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Must be used with an object-based FormView (e.g. CreateView).
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"""
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accepted_media_types = ["text/html", "application/json"]
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def dispatch(self, request, *args, **kwargs):
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if request.get_preferred_type(self.accepted_media_types) is None:
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# No format in common.
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return HttpResponse(
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status_code=406, headers={"Accept": ",".join(self.accepted_media_types)}
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)
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return super().dispatch(request, *args, **kwargs)
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def form_invalid(self, form):
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response = super().form_invalid(form)
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accepted_type = request.get_preferred_type(self.accepted_media_types)
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if accepted_type == "text/html":
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return response
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elif accepted_type == "application/json":
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return JsonResponse(form.errors, status=400)
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def form_valid(self, form):
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# We make sure to call the parent's form_valid() method because
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# it might do some processing (in the case of CreateView, it will
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# call form.save() for example).
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response = super().form_valid(form)
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accepted_type = request.get_preferred_type(self.accepted_media_types)
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if accepted_type == "text/html":
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return response
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elif accepted_type == "application/json":
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data = {
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"pk": self.object.pk,
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}
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return JsonResponse(data)
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.. versionchanged:: 5.2
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The :meth:`.HttpRequest.get_preferred_type` method was added.
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