Django: Forcing admin users to enter at least one item in TabularInline

Question

In my admin for an object Chair I have a TabularInline for an arbitrary number of Desk objects. I want every Chair to always have at least one Desk object associated with it. Is there a way to make the admin interface force the user to enter at least one Desk? Like show an error if no Desk is entered?

Answer 1

Using akaihola's answer, here is a more complete example:

Add this to your forms.py:

from django import forms
from django.forms.models import BaseInlineFormSet

class AtLeastOneRequiredInlineFormSet(BaseInlineFormSet):

    def clean(self):
        """Check that at least one service has been entered."""
        super(AtLeastOneRequiredInlineFormSet, self).clean()
        if any(self.errors):
            return
        if not any(cleaned_data and not cleaned_data.get('DELETE', False)
            for cleaned_data in self.cleaned_data):
            raise forms.ValidationError('At least one item required.')

And then, in your admin.py:

class DeskInline(admin.TabularInline):
    model = Desk
    formset = AtLeastOneRequiredInlineFormSet

class ChairAdmin(admin.ModelAdmin):
    inlines = [DeskInline,]

admin.site.register(Chair, ChairAdmin)