Make filter unique constraint use NULLS NOT DISTINCT

The existing constraint was ineffective as null values were considered distinct, and so two filters with the same content and no overrides were considered different.

This change uses a new PSQL 15 feature unsupported in django currently, and so it is added with raw SQL.

3 files changed, 34 insertions, 26 deletions

diff --git a/pydis_site/apps/api/migrations/0087_unique_constraint_filters.py b/pydis_site/apps/api/migrations/0087_unique_constraint_filters.py
index b2ff91f1..910e7b1b 100644
--- a/pydis_site/apps/api/migrations/0087_unique_constraint_filters.py
+++ b/pydis_site/apps/api/migrations/0087_unique_constraint_filters.py
@@ -1,5 +1,3 @@
-# Generated by Django 3.1.14 on 2022-03-22 16:31
-
 from django.db import migrations, models
 
 
@@ -10,29 +8,18 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
-        migrations.AddConstraint(
-            model_name='filter',
-            constraint=models.UniqueConstraint(fields=(
-                'content',
-                'additional_field',
-                'filter_list',
-                'dm_content',
-                'dm_embed',
-                'infraction_type',
-                'infraction_reason',
-                'infraction_duration',
-                'infraction_channel',
-                'guild_pings',
-                'filter_dm',
-                'dm_pings',
-                'remove_context',
-                'bypass_roles',
-                'enabled',
-                'send_alert',
-                'enabled_channels',
-                'disabled_channels',
-                'enabled_categories',
-                'disabled_categories'
-            ), name='unique_filters'),
+        migrations.RunSQL(
+            "ALTER TABLE api_filter "
+            "ADD CONSTRAINT unique_filters UNIQUE NULLS NOT DISTINCT "
+            "(content, additional_field, filter_list_id, dm_content, dm_embed, infraction_type, infraction_reason, infraction_duration, infraction_channel, guild_pings, filter_dm, dm_pings, remove_context, bypass_roles, enabled, send_alert, enabled_channels, disabled_channels, enabled_categories, disabled_categories)",
+            state_operations=[
+                migrations.AddConstraint(
+                    model_name='filter',
+                    constraint=models.UniqueConstraint(
+                        fields=('content', 'additional_field', 'filter_list', 'dm_content', 'dm_embed', 'infraction_type', 'infraction_reason', 'infraction_duration', 'infraction_channel', 'guild_pings', 'filter_dm', 'dm_pings', 'remove_context', 'bypass_roles', 'enabled', 'send_alert', 'enabled_channels', 'disabled_channels', 'enabled_categories', 'disabled_categories'),
+                        name='unique_filters'
+                    ),
+                ),
+            ],
         ),
     ]
diff --git a/pydis_site/apps/api/serializers.py b/pydis_site/apps/api/serializers.py
index 7f9461ec..8da47802 100644
--- a/pydis_site/apps/api/serializers.py
+++ b/pydis_site/apps/api/serializers.py
@@ -257,6 +257,15 @@ class FilterSerializer(ModelSerializer):
         ) + SETTINGS_FIELDS
         extra_kwargs = _create_filter_meta_extra_kwargs()
 
+    def create(self, validated_data: dict) -> User:
+        """Override the create method to catch violations of the custom uniqueness constraint."""
+        try:
+            return super().create(validated_data)
+        except IntegrityError:
+            raise ValidationError(
+                "Check if a filter with this combination of content and settings already exists in this filter list."
+            )
+
     def to_representation(self, instance: Filter) -> dict:
         """
         Provides a custom JSON representation to the Filter Serializers.
diff --git a/pydis_site/apps/api/tests/test_filters.py b/pydis_site/apps/api/tests/test_filters.py
index cae78cd6..73c8e0d9 100644
--- a/pydis_site/apps/api/tests/test_filters.py
+++ b/pydis_site/apps/api/tests/test_filters.py
@@ -327,3 +327,15 @@ class FilterValidationTests(AuthenticatedAPITestCase):
                     f"{base_filter_list.url()}/{case_fl.id}", data=clean_test_json(filter_list_settings)
                 )
                 self.assertEqual(response.status_code, response_code)
+
+    def test_filter_unique_constraint(self) -> None:
+        test_filter = get_test_sequences()["filter"]
+        test_filter.model.objects.all().delete()
+        test_filter_object = test_filter.model(**test_filter.object)
+        save_nested_objects(test_filter_object, False)
+
+        response = self.client.post(test_filter.url(), data=clean_test_json(test_filter.object))
+        self.assertEqual(response.status_code, 201)
+
+        response = self.client.post(test_filter.url(), data=clean_test_json(test_filter.object))
+        self.assertEqual(response.status_code, 400)