django - update model with FormView and ModelForm

Question

I can't figure out how to use a ModelForm in a FormView so that it updates an already existing instance??

The form POSTs on this URL: r'/object/(?P<pk>)/'

I use a ModelForm (and not directly an UpdateView) because one of the fields is required and I perform a clean on it.

I'd basically like to provide the kwarg instance=... when initializing the form in the FormView (at POST) so that it's bound to the object whose pk is given in the url. But I can't figure out where to do that...

class SaveForm(ModelForm):
    somedata = forms.CharField(required=False)
    class Meta:
        model = SomeModel  # with attr somedata
        fields = ('somedata', 'someotherdata')
    def clean_somedata(self):
        return sometransformation(self.cleaned_data['somedata'])

class SaveView(FormView):
    form_class = SaveForm
    def form_valid(self, form):
        # form.instance here would be == SomeModel.objects.get(pk=pk_from_kwargs)
        form.instance.save()
        return ...

Answer 1

For any further visitors of this thread, yes, you can make a FormView that acts like both a CreateView and an UpdateView. This, despite some opinions of other users, can make a lot of sense if you want to have a single form/URL/page for a web form to save some user data which can be optional but needs to be saved once and only once. You don't want to have 2 URLs/views for this, but just only one page/URL which shows a form, filled with previous data to be updated if a model was already saved by the user.

Think in a kind of "contact" model like this one:

from django.conf import settings
from django.db import models


class Contact(models.Model):
    """
    Contact details for a customer user.
    """
    user = models.OneToOneField(settings.AUTH_USER_MODEL)
    street = models.CharField(max_length=100, blank=True)
    number = models.CharField(max_length=5, blank=True)
    postal_code = models.CharField(max_length=7, blank=True)
    city = models.CharField(max_length=50, blank=True)
    phone = models.CharField(max_length=15)
    alternative_email = models.CharField(max_length=254)

So, you write a ModelForm for it, like this:

from django import forms

from .models import Contact


class ContactForm(forms.ModelForm):
    class Meta:
        model = Contact
        exclude = ('user',)  # We'll set the user later.

And your FormView with both "create" and "update" capabilities will look like this:

from django.core.urlresolvers import reverse
from django.views.generic.edit import FormView

from .forms import ContactForm
from .models import Contact


class ContactView(FormView):
    template_name = 'contact.html'
    form_class = ContactForm
    success_url = reverse('MY_URL_TO_REDIRECT')

    def get_form(self, form_class):
        """
        Check if the user already saved contact details. If so, then show
        the form populated with those details, to let user change them.
        """
        try:
            contact = Contact.objects.get(user=self.request.user)
            return form_class(instance=contact, **self.get_form_kwargs())
        except Contact.DoesNotExist:
            return form_class(**self.get_form_kwargs())

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

You don't even need to use a pk in the URL of this example, because the object is retrieved from the DB via the user one-to-one field. If you have a case similar than this, in which the model to be created/updated has a unique relationship with the user, it is very easy.

Hope this helps somebody...

Cheers.

Answer 2

After some discussion with you, I still don't see why you can't use an UpdateView. It seems like a very simple use case if I understand correctly. You have a model that you want to update. And you have a custom form to do cleaning before saving it to that model. Seems like an UpdateView would work just fine. Like this:

class SaveForm(ModelForm):
    somedata = forms.CharField(required=False)

    class Meta:
        model = SomeModel  # with attr somedata
        fields = ('somedata', 'someotherdata')

    def clean_somedata(self):
        return sometransformation(self.cleaned_data['somedata'])


class SaveView(UpdateView):
    template_name = 'sometemplate.html'
    form_class = SaveForm
    model = SomeModel

    # That should be all you need. If you need to do any more custom stuff 
    # before saving the form, override the `form_valid` method, like this:

    def form_valid(self, form):
        self.object = form.save(commit=False)

        # Do any custom stuff here

        self.object.save()

        return render_to_response(self.template_name, self.get_context_data())

Of course, if I am misunderstanding you, please let me know. You should be able to get this to work though.

Answer 3

You can use the post method of FormView to get the posted data and save to model using form.save(). Hope this will help.

Try this

    class SaveForm(ModelForm):
    somedata = forms.CharField(required=False)

    class Meta:
        model = SomeModel  # with attr somedata
        fields = ('somedata', 'someotherdata')

    def __init__(self, *args, **kwargs):
        super(SaveForm, self).__init__(*args, **kwargs)

    def save(self, id):
        print id   #this id will be sent from the view
        instance = super(SaveForm, self).save(commit=False)
        instance.save()
        return instance


class SaveView(FormView):
    template_name = 'sometemplate.html'
    form_class = SaveForm

    def post(self, request, *args, **kwargs):

        form = self.form_class(request.POST)

        if form.is_valid():
            form.save(kwargs.get('pk'))
        else:
            return self.form_invalid(form)