Django ModelForm - replacement for form_for_model & form_for_instance

Each commit, Django gets more amazing.

I wrote about newforms library before. The library was a big step in Django form displaying and validating.

The first approach was to use forms.form_for_model() and forms.form_for_instance() respectively.

As Django programmer I found this a little confusing. Both were similar. The only difference was that form_for_instance() took an object instance for saving instead
of creating a new one. Recently django developers came up with a great idea - forms.ModelForm which combines both into one. It's great!

Just take a look at the example below.
Assume you want to create a new view function for creating & editing an object.
You only want to edit 3 fields (name, last_name, status). Also, you've created a
customized field type for "status", and want to use that.

Scenario #1: (forms.form_for_model && forms.form_for_instance)

def f_callback(field, **kwargs):
    if field.name == "status":
        return MyStatusField(**kwargs)
    else:
        return field.formfield(**kwargs)

def create_edit_customer(request, customer_id=None):

    # check if object_id is None and if object exists
    if object_id is None:
        CustomerForm = forms.form_for_model(Customer,
        formfield_callback=f_callback,
        fields=('name','last_name','status')
    else:
        customer = get_object_or_404(Customer, id=customer_id)
        CustomerForm = forms.form_for_instance(customer,
        formfield_callback=f_callback,
        fields=('name','last_name','status')

    if request.method == "POST":
        form = CustomerForm(request.POST)
        if form.is_valid():
            form.save()
            return HttpResponseRedirect('customer/added/')
    else:
        form = CustomerForm()

    return render_to_response("customers/customer_form.html", {'form' : form })

You could create your own form_for_model & form_for_instance subclass (using forms.BaseForm for example), but it would be too complicated. Hope you don't use this form often :-)

Scenario #2 (ModelForm)

1. Longer version.

class CustomerModelForm(forms.ModelForm):

    class Meta:
        model = Customer
        fields = ('name','last_name','status')

        status = MyCustomerField()

def create_edit_customer(request, customer_id=None):

    if customer_id is not None:
        customer = get_object_or_404(Customer, id=customer_id)
    else:
        customer = None


    if request.method == "POST":
        form = CustomerModelForm(data=request.POST, instance=customer)
        if form.is_valid():
            form.save()
            return HttpResponseRedirect("/customer/added/")
        else:
            form = CustomerModelForm(instance=customer)

    return render_to_response("customers/customer_form.html", {'form' : form })

2. Shorter version.

class CustomerModelForm(forms.ModelForm):

    class Meta:
        model = Customer
        fields = ('name','last_name','status')

    status = MyCustomerField()

def create_edit_customer(request, customer_id=None):

    if customer_id is not None:
        customer = get_object_or_404(Customer, id=customer_id)
    else:
        customer = None

    form = CustomerModelForm(data=request.POST or None, instance=customer)

    if form.is_valid():
        form.save()
        return HttpResponseRedirect("/customer/added/")

    return render_to_response("customers/customer_form.html", {'form' : form }

We are using one form class for editing & creating objects.
We can also subclass CustomerModelForm and edit/change the way the form looks
and behave (by adding field clean() method.

Django forms library looks better each day :-)