Daniel's answer is excellent and it worked for me on one project, but then I realized due to the way Django forms work, if you are using can_delete and check the delete box while saving, it's possible to validate w/o any orders (in this case).
I spent a while trying to figure out how to prevent that from happening. The first situation was easy - don't include the forms that are going to get deleted in the count. The second situation was trickier...if all the delete boxes are checked, then clean
wasn't being called.
The code isn't exactly straightforward, unfortunately. The clean
method is called from full_clean
which is called when the error
property is accessed. This property is not accessed when a subform is being deleted, so full_clean
is never called. I'm no Django expert, so this might be a terrible way of doing it, but it seems to work.
Here's the modified class:
class InvoiceOrderInlineFormset(forms.models.BaseInlineFormSet):
def is_valid(self):
return super(InvoiceOrderInlineFormset, self).is_valid() and \
not any([bool(e) for e in self.errors])
def clean(self):
# get forms that actually have valid data
count = 0
for form in self.forms:
try:
if form.cleaned_data and not form.cleaned_data.get('DELETE', False):
count += 1
except AttributeError:
# annoyingly, if a subform is invalid Django explicity raises
# an AttributeError for cleaned_data
pass
if count < 1:
raise forms.ValidationError('You must have at least one order')