API should 400 on unique violations

src/documents/serialisers.py

@@ -68,6 +68,25 @@ def get_slug(self, obj):
 
     slug = SerializerMethodField()
 
+    def validate(self, data):
+        # see https://github.com/encode/django-rest-framework/issues/7173
+        name = data["name"] if "name" in data else self.instance.name
+        owner = (
+            data["owner"]
+            if "owner" in data
+            else self.user
+            if hasattr(self, "user")
+            else None
+        )
+        if ("name" in data or "owner" in data) and self.Meta.model.objects.filter(
+            name=name,
+            owner=owner,
+        ).exists():
+            raise serializers.ValidationError(
+                {"error": "Object violates owner / name unique constraint"},
+            )
+        return data
+
     def validate_match(self, match):
         if (
             "matching_algorithm" in self.initial_data
@@ -188,15 +207,14 @@ def update(self, instance, validated_data):
             self._set_permissions(validated_data["set_permissions"], instance)
         if "owner" in validated_data and "name" in self.Meta.fields:
             name = validated_data["name"] if "name" in validated_data else instance.name
-            print(name)
             not_unique = (
                 self.Meta.model.objects.exclude(pk=instance.pk)
                 .filter(owner=validated_data["owner"], name=name)
                 .exists()
             )
             if not_unique:
                 raise serializers.ValidationError(
-                    "Object violates owner / name unique constraint",
+                    {"error": "Object violates owner / name unique constraint"},
                 )
         return super().update(instance, validated_data)
 

src/documents/tests/test_api.py

@@ -1850,26 +1850,38 @@ def test_tag_unique_name_and_owner(self):
         user1 = User.objects.create_user(username="test1")
         user2 = User.objects.create_user(username="test2")
 
-        self.client.post("/api/tags/", {"name": "tag 1"}, format="json")
+        response = self.client.post("/api/tags/", {"name": "tag 1"}, format="json")
+        self.assertEqual(response.status_code, status.HTTP_201_CREATED)
 
-        with transaction.atomic():
-            with self.assertRaises(IntegrityError):
-                self.client.post("/api/tags/", {"name": "tag 1"}, format="json")
+        response = self.client.post("/api/tags/", {"name": "tag 1"}, format="json")
+        self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
 
         self.client.post(
             "/api/tags/",
             {"name": "tag 2", "owner": user1.pk},
             format="json",
         )
 
-        try:
-            self.client.post(
-                "/api/tags/",
-                {"name": "tag 2", "owner": user2.pk},
-                format="json",
-            )
-        except IntegrityError as e:
-            assert False, f"Exception {e}"
+        response = self.client.post(
+            "/api/tags/",
+            {"name": "tag 2", "owner": user1.pk},
+            format="json",
+        )
+        self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+
+        self.client.post(
+            "/api/tags/",
+            {"name": "tag 3", "owner": user1.pk},
+            format="json",
+        )
+
+        response = self.client.post(
+            "/api/tags/",
+            {"name": "tag 3", "owner": user2.pk},
+            format="json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_201_CREATED)
 
     def test_tag_unique_name_and_owner_enforced_on_update(self):
         user1 = User.objects.create_user(username="test1")