How to display a user's get_full_name() instead of the username in a Django model form?

This can be done several ways.

Create a proxy subclass of User and override its __unicode__() method to return user's full name.

class UserFullName(User):
    class Meta:
        proxy = True

    def __unicode__(self):
        return self.get_full_name()

Now in your model form, use UserFullName to retrieve users.

class BookForm(forms.ModelForm):
    author = forms.ModelChoiceField(queryset=UserFullName.objects.all())
    class Meta:
        model = Book

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Another way is to dynamically populate choices in form's constructor.

class BookForm(forms.ModelForm):

    def __init__(self, *args, **kwargs):
        super(BookForm, self).__init__(*args, **kwargs)
        users = User.objects.all()
        self.fields['author'].choices = [(user.pk, user.get_full_name()) for user in users]

    class Meta:
        model = Book

---

Perhaps, the most "djangonic" way is demonstrated by lazerscience as an answer to the similar question Django forms: how to dynamically create ModelChoiceField labels. It subclasses ModelChoiceField and overrides its label_from_instance() method that is intended to provide choice labels.

class UserFullnameChoiceField(forms.ModelChoiceField):
    def label_from_instance(self, obj):
        return smart_unicode(obj.get_full_name())

class BookForm(forms.ModelForm):
    author = UserFullnameChoiceField(queryset=User.objects.all())

    class Meta:
        model = Book