Unify frozen fields logic into serializer mixin (#1169)

Additionally, implement frozen fields on the offensive message
serializer.

1 files changed, 31 insertions, 3 deletions

diff --git a/pydis_site/apps/api/serializers.py b/pydis_site/apps/api/serializers.py
index 2186b02c..87fd6190 100644
--- a/pydis_site/apps/api/serializers.py
+++ b/pydis_site/apps/api/serializers.py
@@ -2,6 +2,7 @@
 from datetime import timedelta
 from typing import Any
 
+from django.db import models
 from django.db.models.query import QuerySet
 from django.db.utils import IntegrityError
 from rest_framework.exceptions import NotFound
@@ -35,6 +36,30 @@ from .models import (
     User
 )
 
+class FrozenFieldsMixin:
+    """
+    Serializer mixin that allows adding non-updateable fields to a serializer.
+
+    To use, inherit from the mixin and specify the fields that should only be
+    written to on creation in the `frozen_fields` attribute of the `Meta` class
+    in a serializer.
+
+    See also the DRF discussion for this feature at
+    https://github.com/encode/django-rest-framework/discussions/8606, which may
+    eventually provide an official way to implement this.
+    """
+
+    def update(self, instance: models.Model, validated_data: dict) -> models.Model:
+        """Validate that no frozen fields were changed and update the instance."""
+        for field_name in getattr(self.Meta, 'frozen_fields', ()):
+            if field_name in validated_data:
+                raise ValidationError(
+                    {
+                        field_name: ["This field cannot be updated."]
+                    }
+                )
+        return super().update(instance, validated_data)
+
 
 class BotSettingSerializer(ModelSerializer):
     """A class providing (de-)serialization of `BotSetting` instances."""
@@ -426,7 +451,7 @@ class FilterListSerializer(ModelSerializer):
 #  endregion
 
 
-class InfractionSerializer(ModelSerializer):
+class InfractionSerializer(FrozenFieldsMixin, ModelSerializer):
     """A class providing (de-)serialization of `Infraction` instances."""
 
     class Meta:
@@ -447,6 +472,7 @@ class InfractionSerializer(ModelSerializer):
             'dm_sent',
             'jump_url'
         )
+        frozen_fields = ('id', 'inserted_at', 'type', 'user', 'actor', 'hidden')
 
     def validate(self, attrs: dict) -> dict:
         """Validate data constraints for the given data and abort if it is invalid."""
@@ -683,7 +709,7 @@ class NominationEntrySerializer(ModelSerializer):
         fields = ('nomination', 'actor', 'reason', 'inserted_at')
 
 
-class NominationSerializer(ModelSerializer):
+class NominationSerializer(FrozenFieldsMixin, ModelSerializer):
     """A class providing (de-)serialization of `Nomination` instances."""
 
     entries = NominationEntrySerializer(many=True, read_only=True)
@@ -703,9 +729,10 @@ class NominationSerializer(ModelSerializer):
             'entries',
             'thread_id'
         )
+        frozen_fields = ('id', 'inserted_at', 'user', 'ended_at')
 
 
-class OffensiveMessageSerializer(ModelSerializer):
+class OffensiveMessageSerializer(FrozenFieldsMixin, ModelSerializer):
     """A class providing (de-)serialization of `OffensiveMessage` instances."""
 
     class Meta:
@@ -713,3 +740,4 @@ class OffensiveMessageSerializer(ModelSerializer):
 
         model = OffensiveMessage
         fields = ('id', 'channel_id', 'delete_date')
+        frozen_fields = ('id', 'channel_id')