Fix invalid similarity checker

Author: WaVEV

django_mongodb_backend/indexes.py

@@ -159,10 +159,12 @@ def check(self, model, connection):
         for func in similarities:
             if func not in self.ALLOWED_SIMILARITY_FUNCTIONS:
                 errors.append(
-                    f"{func} isn't a valid similarity function, options "
-                    f"'are {','.join(self.ALLOWED_SIMILARITY_FUNCTIONS)}",
-                    obj=self,
-                    id=f"{error_id_prefix}.E003",
+                    Error(
+                        f"{func} isn't a valid similarity function, options "
+                        f"are {', '.join(sorted(self.ALLOWED_SIMILARITY_FUNCTIONS))}",
+                        obj=self,
+                        id=f"{error_id_prefix}.E004",
+                    )
                 )
         for field_name, _ in self.fields_orders:
             field_ = model._meta.get_field(field_name)

tests/system_checks/tests.py

@@ -77,6 +77,28 @@ class Meta:
             ],
         )
 
+    def test_vectorsearch_invalid_similarity_function(self):
+        class Article(models.Model):
+            vector_data = ArrayField(models.DecimalField(), size=10)
+
+            class Meta:
+                indexes = [
+                    VectorSearchIndex(fields=["vector_data"], similarities="sum"),
+                ]
+
+        errors = checks.run_checks(app_configs=self.apps.get_app_configs(), databases={"default"})
+        self.assertEqual(
+            errors,
+            [
+                checks.Error(
+                    "sum isn't a valid similarity function, "
+                    "options are cosine, dotProduct, euclidean",
+                    id="django_mongodb_backend.indexes.VectorSearchIndex.E004",
+                    obj=Article._meta.indexes[0],
+                )
+            ],
+        )
+
     def test_vectorsearch(self):
         class Article(models.Model):
             vector_data = ArrayField(models.DecimalField(), size=10)