Django form field validation - How to tell if operation is insert or update?

Question

I'm trying to do this in Django: When saving an object in the Admin I want to save also another object of a different type based on one of the fields in my fist object. In order to do this I must check if that second object already exists and return an validation error only for the particular field in the first object if it does. My problem is that I want the validation error to appear in the field only if the operation is insert.

How do I display a validation error for a particular admin form field based on knowing if the operation is update or insert?

P.S. I know that for a model validation this is impossible since the validator only takes the value parameter, but I think it should be possible for form validation.

Answer 1

This ca be done by writing a clean_[name_of_field] method in a Django Admin Form. The insert or update operation can be checked by testing self.instance.pk.

class EntityAdminForm(forms.ModelForm):
    def clean_field(self):
        field = self.cleaned_data['field']
        insert = self.instance.pk == None
        if insert:
            raise forms.ValidationError('Some error message!')
        else:
            pass
        return field

class EntityAdmin(admin.ModelAdmin):
    form = EntityAdminForm

You have to use then the EntityAdmin class when registering the Entity model with the Django admin:

admin.site.register(Entity, EntityAdmin)