Provide a way for model formsets to know how many records will be created

[mstevens@…]

This is a feature request - please provide an easy way for model formsets to know how many records will be created.

As an example, I'm trying to write a clean() method for an inlineformset that checks that the database will always contain at least one model row when saved. The information to do this doesn't seem to be available.

[Aymeric Augustin]

Unfortunately, this isn't something you can know in clean().

The sequence is as follows:

• 1) clean(), well, cleans data received from the browser,
• 2) existing instances present in the form, if any, are loaded from the database,
• 3) existing instances are saved with the modifications and new instances are created.

That's why it isn't possible to know how many records will be created until step 2. However, you could check len(form.new_objects) after saving.

[Florian Apolloner]

One (untested) possibility is:

def clean(self):
  super(BlaForm, self).clean()
  c = 0
  for f in self.extra_forms:
    if f.has_changed() and not self._should_delete_form(f):
      c += 1

After that c should tell you how many objects will get created, see save_new_objects and save_existing_objects for more info.