misc: don't get concrete class when looking at placeholder emptiness (#17645)

combo/data/models.py

@@ -258,8 +258,8 @@ class Page(models.Model):
     def is_visible(self, user=None):
         return element_is_visible(self, user=user)
 
-    def get_cells(self):
-        return CellBase.get_cells(page_id=self.id)
+    def get_cells(self, **kwargs):
+        return CellBase.get_cells(page_id=self.id, **kwargs)
 
     def get_serialized_page(self):
         cells = [x for x in self.get_cells() if x.placeholder and not x.placeholder.startswith('_')]
@@ -392,9 +392,12 @@ class CellBase(models.Model):
         return cell_types
 
     @classmethod
-    def get_cells(cls, **kwargs):
+    def get_cells(cls, concrete=True, **kwargs):
         """Returns a queryset of cells of various classes matching **kwargs"""
-        return cls.objects.filter(**kwargs).order_by('order').select_subclasses()
+        queryset = cls.objects.filter(**kwargs).order_by('order')
+        if not concrete:
+            return queryset
+        return queryset.select_subclasses()
 
     def get_reference(self):
         "Returns a string that can serve as a unique reference to a cell"""

combo/public/templatetags/combo.py

@@ -219,4 +219,4 @@ def get_group(group_list, group_name):
 
 @register.filter(name='is_empty_placeholder')
 def is_empty_placeholder(page, placeholder_name):
-    return len([x for x in page.get_cells() if x.placeholder == placeholder_name]) == 0
+    return not page.get_cells(concrete=False).filter(placeholder=placeholder_name).exists()