how to limit django admin inline formsets
http://docs.djangoproject.com/en/dev/ref/contrib/admin/#inlinemodeladmin-options
Specify max_num in your Inline definition to limit the number.
extra specifies how many blank inlines to show.
Is the 1 inline required? As in you want to trigger a validation error if table B isn't filled with at least 1 row?
The enabling / disabling of the add button in an inline is managed through the _has_add_permission method
you could add to your inline class:
def _has_add_permission(self, request, obj=None): # add/remove possibility to add a line to an inline if obj.table_b_items.count() < 5: return True else: return False