What is the difference between use fields attribute and use a FormClass in Django CreateView?

Question

What is the difference between use:

class FooCreateView(CreateView):
   model = Foo
   fields = (f,o,o)

and

class FooCreateView(CreateView):
   model = Foo
   form_class = FooForm

Answer 1

The difference is that in the second you need to define a FooForm class that must inherit from Django ModelForm class and have a model = Foo, this mechanism allows you to implement extra validations over your form (i.e. by defining methods like: def clean_f(self), def clean_o(self))

As you can see, you don't need to specify the fields attribute in the CreateView subclasss if using a form_class, because Django will take the form_class fields and use it.

Example:

models.py

from django.db import models

class Foo(models.Model):
    f = models.CharField(max_length=10)

forms.py

from django import forms
from appname.models import Foo

class FooForm(forms.ModelForm):
    class Meta:
        model = Foo
        fields = '__all__'  # shortcut to add all Foo fields.

    def clean_f(self):
        if 'M' not in self.cleaned_data['f']:
            raise forms.ValidationError('M char must be in f attribute')
        return self.cleaned_data['f']

views.py

from django.views.edit import CreateView
from appname.forms import FooForm

class FooCreateView(CreateView):
    model = Foo
    form_class = FooForm

This will raise a ValidationError if you try to save a Foo instance which does not contains a 'M' in their f attribute.