# Documentazione Django 6.0.7

# 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:

`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 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` so `template_name` can be used here.

- The default implementation for `form_valid()` simply redirects to the `success_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.

Nota

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 AuthorCreateView(CreateView):
        model = Author
        fields = ["name"]

    class AuthorUpdateView(UpdateView):
        model = Author
        fields = ["name"]

    class AuthorDeleteView(DeleteView):
        model = Author
        success_url = reverse_lazy("author-list")

Nota

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:

`urls.py`

    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"),
    ]

Nota

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

In this example:

- `CreateView` and `UpdateView` use `myapp/author_form.html`

- `DeleteView` uses `myapp/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:

`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.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"]

The above example assumes that if the client supports `text/html`, that they would prefer it. However, this may not always be true. When requesting a `.css` file, many browsers will send the header `Accept: text/css,*/*;q=0.1`, indicating that they would prefer CSS, but anything else is fine. This means `request.accepts("text/html")` will be `True`.

To determine the correct format, taking into consideration the client’s preference, use `django.http.HttpRequest.get_preferred_type()`:

    class JsonableResponseMixin:
        """
        Mixin to add JSON support to a form.
        Must be used with an object-based FormView (e.g. CreateView).
        """

        accepted_media_types = ["text/html", "application/json"]

        def dispatch(self, request, *args, **kwargs):
            if request.get_preferred_type(self.accepted_media_types) is None:
                # No format in common.
                return HttpResponse(
                    status_code=406, headers={"Accept": ",".join(self.accepted_media_types)}
                )

            return super().dispatch(request, *args, **kwargs)

        def form_invalid(self, form):
            response = super().form_invalid(form)
            accepted_type = self.request.get_preferred_type(self.accepted_media_types)
            if accepted_type == "text/html":
                return response
            elif accepted_type == "application/json":
                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)
            accepted_type = self.request.get_preferred_type(self.accepted_media_types)
            if accepted_type == "text/html":
                return response
            elif accepted_type == "application/json":
                data = {
                    "pk": self.object.pk,
                }
                return JsonResponse(data)