django - how to check in a clean method of a form whether it is an insert or an update

Question

Hi,

I have a form where I validate in the clean method whether a ProjectMembership object already exist, that has the same values for project and member. This is due that I have in the ProjectMembership model defined a unique_together constraint for project and member. This works fine actually.

class ProjectMembershipForm(forms.ModelForm):

    project = forms.ModelChoiceField(Project.objects, widget=HiddenInput())

    class Meta:
        model = ProjectMembership

    def clean(self):
        cleaned_data = self.cleaned_data

        project = cleaned_data.get("project")
        member = cleaned_data.get("member")

        print ProjectMembership.objects.filter(project=project, member=member).count()
        if ProjectMembership.objects.filter(project=project, member=member).count() > 0:
            del cleaned_data["project"]
            del cleaned_data["member"]
            raise forms.ValidationError('The user "%s" is already part of the project team for project "%s".' % (member, project))
        return cleaned_data

But now I'm asking myself how I can judge in the clean method whether the user tries to create a new relationship or update a relationship. Because with this clean method it is not possible to do an update, since it returns the error message that the entry already exist.

Answer 1

You can try changing this:

if ProjectMembership.objects.filter(project=project, member=member).count() > 0:

to something like this:

if ProjectMembership.objects.filter(project=project, member=member).exclude(pk = self.instance.id).count() > 0:

actually you need to check if self.instance is not None before you use it in exclude but hopefully this little snippet gave you some idea how yo can accomplish your task without having forms duplicated.