Unify frozen fields logic into serializer mixin (#1169)

Additionally, implement frozen fields on the offensive message
serializer.

2 files changed, 9 insertions, 1 deletions

diff --git a/pydis_site/apps/api/tests/test_nominations.py b/pydis_site/apps/api/tests/test_nominations.py
index 7fe2f0a8..e4dfe36a 100644
--- a/pydis_site/apps/api/tests/test_nominations.py
+++ b/pydis_site/apps/api/tests/test_nominations.py
@@ -254,7 +254,7 @@ class NominationTests(AuthenticatedAPITestCase):
     def test_returns_400_on_frozen_field_update(self):
         url = reverse('api:bot:nomination-detail', args=(self.active_nomination.id,))
         data = {
-            'user': "Theo Katzman"
+            'user': 1234
         }
 
         response = self.client.patch(url, data=data)
diff --git a/pydis_site/apps/api/tests/test_offensive_message.py b/pydis_site/apps/api/tests/test_offensive_message.py
index d01231f1..2dc60bc3 100644
--- a/pydis_site/apps/api/tests/test_offensive_message.py
+++ b/pydis_site/apps/api/tests/test_offensive_message.py
@@ -156,6 +156,14 @@ class UpdateOffensiveMessageTestCase(AuthenticatedAPITestCase):
             delta=datetime.timedelta(seconds=1),
         )
 
+    def test_updating_write_once_fields(self):
+        """Fields such as the channel ID may not be updated."""
+        url = reverse('api:bot:offensivemessage-detail', args=(self.message.id,))
+        data = {'channel_id': self.message.channel_id + 1}
+        response = self.client.patch(url, data=data)
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(response.json(), {'channel_id': ["This field cannot be updated."]})
+
     def test_updating_nonexistent_message(self):
         url = reverse('api:bot:offensivemessage-detail', args=(self.message.id + 1,))
         data = {'delete_date': self.in_one_week}