save some fixes

src/documents/models.py

@@ -117,7 +117,7 @@ class Tag(MatchingModel, TreeNodeModel):
         verbose_name_plural = _("tags")
 
     def subtree_height(self, node: TreeNodeModel) -> int:
-        children = list(node.children)
+        children = list(node.get_children())
         if not children:
             return 0
         return 1 + max(self.subtree_height(child) for child in children)

src/documents/serialisers.py

@@ -544,6 +544,14 @@ class TagSerializer(MatchingModelSerializer, OwnedObjectSerializer):
     def get_children(self, obj):
         return obj.get_children_pks()
 
+    # map to treenode's tn_parent
+    parent = serializers.PrimaryKeyRelatedField(
+        queryset=Tag.objects.all(),
+        allow_null=True,
+        required=False,
+        source="tn_parent",
+    )
+
     class Meta:
         model = Tag
         fields = (
@@ -579,13 +587,13 @@ class TagSerializer(MatchingModelSerializer, OwnedObjectSerializer):
             # Temporarily set parent on the instance if updating and use model clean()
             original_parent = self.instance.parent
             try:
-                self.instance.tn_parent = parent
+                self.instance.set_parent(parent)
                 self.instance.clean()
-            except ValidationError as e:
+            except ValueError as e:
                 logger.debug("Tag parent validation failed: %s", e)
                 raise serializers.ValidationError({"parent": _("Invalid parent tag.")})
             finally:
-                self.instance.tn_parent = original_parent
+                self.instance.set_parent(original_parent)
         else:
             # For new instances, create a transient Tag and validate
             temp = Tag(tn_parent=parent)
@@ -1070,7 +1078,7 @@ class DocumentSerializer(
             tag_parents_being_removed = [
                 tag
                 for tag in instance.tags.all()
-                if tag not in validated_data["tags"] and tag.children.count() > 0
+                if tag not in validated_data["tags"] and tag.get_children_count() > 0
             ]
             validated_data["tags"] = [
                 tag

src/documents/tests/test_tag_hierarchy.py

@@ -144,7 +144,7 @@ class TestTagHierarchy(APITestCase):
             format="json",
         )
         assert resp.status_code == 400
-        assert "parent" in resp.data
+        assert "Cannot set parent to a descendant" in str(resp.data["non_field_errors"])
 
     def test_max_depth_on_create(self):
         a = Tag.objects.create(name="A1")
@@ -182,7 +182,7 @@ class TestTagHierarchy(APITestCase):
 
         x = Tag.objects.create(name="X2")
         y = Tag.objects.create(name="Y2", tn_parent=x)
-        assert y.parent_id == x.id
+        assert y.parent_pk == x.pk
 
         # Moving X under D would make deepest node Y exceed depth 5 -> reject
         resp_fail = self.client.patch(
@@ -191,7 +191,9 @@ class TestTagHierarchy(APITestCase):
             format="json",
         )
         assert resp_fail.status_code == 400
-        assert "parent" in resp_fail.data
+        assert "Maximum nesting depth exceeded" in str(
+            resp_fail.data["non_field_errors"],
+        )
 
         # Moving X under C (depth 3) should be allowed (deepest becomes 5)
         resp_ok = self.client.patch(