fix: bug with some descendant counts

openedx_tagging/core/tagging/models/base.py

@@ -458,7 +458,7 @@ def _get_filtered_tags_one_level(
             qs = self.tag_set.filter(parent=None).annotate(depth=Value(0))
             qs = qs.annotate(parent_value=Value(None, output_field=models.CharField()))
         qs = qs.annotate(child_count=models.Count("children", distinct=True))
-        qs = qs.annotate(grandchild_count=models.Count("children__children"))
+        qs = qs.annotate(grandchild_count=models.Count("children__children", distinct=True))
         qs = qs.annotate(great_grandchild_count=models.Count("children__children__children"))
         qs = qs.annotate(descendant_count=F("child_count") + F("grandchild_count") + F("great_grandchild_count"))
         # Filter by search term:
@@ -520,7 +520,9 @@ def _get_filtered_tags_deep(
             qs = qs.filter(pk__in=matching_ids)
             qs = qs.annotate(
                 child_count=models.Count("children", filter=Q(children__pk__in=matching_ids), distinct=True),
-                grandchild_count=models.Count("children__children", filter=Q(children__children__pk__in=matching_ids)),
+                grandchild_count=models.Count(
+                    "children__children", filter=Q(children__children__pk__in=matching_ids), distinct=True,
+                ),
                 great_grandchild_count=models.Count(
                     "children__children__children",
                     filter=Q(children__children__children__pk__in=matching_ids),
@@ -534,7 +536,7 @@ def _get_filtered_tags_deep(
             # frontend.
         else:
             qs = qs.annotate(child_count=models.Count("children", distinct=True))
-            qs = qs.annotate(grandchild_count=models.Count("children__children"))
+            qs = qs.annotate(grandchild_count=models.Count("children__children", distinct=True))
             qs = qs.annotate(great_grandchild_count=models.Count("children__children__children"))
             qs = qs.annotate(descendant_count=F("child_count") + F("grandchild_count") + F("great_grandchild_count"))
 

tests/openedx_tagging/core/tagging/test_models.py

@@ -550,6 +550,37 @@ def test_tree_sort(self) -> None:
             "  azure (ALPHABET) (children: 0)",
         ]
 
+    def test_descendant_counts(self) -> None:
+        """
+        Test getting the descendant count on a taxonomy known to cause aggregation
+        bugs unless the aggregations are correctly specified with distinct=True
+
+        https://docs.djangoproject.com/en/5.0/topics/db/aggregation/#combining-multiple-aggregations
+        """
+        taxonomy = api.create_taxonomy("ESDC Subset")
+        api.add_tag_to_taxonomy(taxonomy, "Interests")  # root tag
+        api.add_tag_to_taxonomy(taxonomy, "Holland Codes", parent_tag_value="Interests")  # child tag
+        # Create the grandchild tag:
+        g_tag = api.add_tag_to_taxonomy(taxonomy, "Interests - Holland Codes", parent_tag_value="Holland Codes")
+        # Create the 6 great-grandchild tags:
+        api.add_tag_to_taxonomy(taxonomy, "Artistic", parent_tag_value=g_tag.value)
+        api.add_tag_to_taxonomy(taxonomy, "Conventional", parent_tag_value=g_tag.value)
+        api.add_tag_to_taxonomy(taxonomy, "Enterprising", parent_tag_value=g_tag.value)
+        api.add_tag_to_taxonomy(taxonomy, "Investigative", parent_tag_value=g_tag.value)
+        api.add_tag_to_taxonomy(taxonomy, "Realistic", parent_tag_value=g_tag.value)
+        api.add_tag_to_taxonomy(taxonomy, "Social", parent_tag_value=g_tag.value)
+
+        result = pretty_format_tags(taxonomy.get_filtered_tags(depth=1, include_counts=True))
+        assert result == [
+            "Interests (None) (used: 0, children: 1 + 7)", # 1 child + 1 grandchild and 6 great grandchild tags = 8 total
+        ]
+        result2 = pretty_format_tags(taxonomy.get_filtered_tags(depth=None, include_counts=True))
+        assert result2 == [
+            "Interests (None) (used: 0, children: 1 + 7)",
+            "  Holland Codes (Interests) (used: 0, children: 1 + 6)",
+            "    Interests - Holland Codes (Holland Codes) (used: 0, children: 6)",
+        ]
+
 
 class TestFilteredTagsFreeTextTaxonomy(TestCase):
     """