Added system check for similarities and vector fields count mismatch.

Author: WaVEV

django_mongodb_backend/indexes.py

@@ -185,6 +185,7 @@ def check(self, model, connection):
                     )
                 )
         viewed = set()
+        expected_similarities = 0
         for field_name, _ in self.fields_orders:
             if field_name in viewed:
                 errors.append(
@@ -197,9 +198,11 @@ def check(self, model, connection):
                         id=f"{self._error_id_prefix}.E005",
                     )
                 )
+                continue
             viewed.add(field_name)
             field_ = model._meta.get_field(field_name)
             if isinstance(field_, ArrayField):
+                expected_similarities += 1
                 try:
                     int(field_.size)
                 except (ValueError, TypeError):
@@ -235,6 +238,22 @@ def check(self, model, connection):
                             id=f"{self._error_id_prefix}.E003",
                         )
                     )
+        if isinstance(self.similarities, list) and expected_similarities != len(self.similarities):
+            given_similarities = len(self.similarities)
+            similarity_function_text = (
+                "similarities functions" if given_similarities != 1 else "similarity function"
+            )
+            errors.append(
+                Error(
+                    f"An Atlas vector search index requires the same number of similarities and "
+                    f"vector fields, but {expected_similarities} "
+                    f"{similarity_function_text} were expected and "
+                    f"{given_similarities} {'were' if given_similarities != 1 else 'was'} "
+                    "provided.",
+                    obj=self,
+                    id=f"{self._error_id_prefix}.E006",
+                )
+            )
         return errors
 
     def deconstruct(self):

tests/indexes_/test_checks.py

@@ -213,6 +213,59 @@ class Meta:
             ],
         )
 
+    def test_invalid_number_similarity_function_singular(self):
+        class Article(models.Model):
+            vector_data = ArrayField(models.DecimalField(), size=10)
+
+            class Meta:
+                indexes = [
+                    VectorSearchIndex(
+                        fields=["vector_data"],
+                        similarities=["dotProduct", "cosine"],
+                    )
+                ]
+
+        errors = checks.run_checks(app_configs=self.apps.get_app_configs(), databases={"default"})
+        self.assertEqual(
+            errors,
+            [
+                checks.Error(
+                    "An Atlas vector search index requires the same number of similarities "
+                    "and vector fields, but 1 similarity function were expected and 2 "
+                    "were provided.",
+                    id="django_mongodb_backend.indexes.VectorSearchIndex.E006",
+                    obj=Article._meta.indexes[0],
+                ),
+            ],
+        )
+
+    def test_invalid_number_similarity_function_plural(self):
+        class Article(models.Model):
+            vector1 = ArrayField(models.DecimalField(), size=10)
+            vector2 = ArrayField(models.DecimalField(), size=10)
+
+            class Meta:
+                indexes = [
+                    VectorSearchIndex(
+                        fields=["vector1", "vector2"],
+                        similarities=["dotProduct"],
+                    )
+                ]
+
+        errors = checks.run_checks(app_configs=self.apps.get_app_configs(), databases={"default"})
+        self.assertEqual(
+            errors,
+            [
+                checks.Error(
+                    "An Atlas vector search index requires the same number of similarities "
+                    "and vector fields, but 2 similarities functions were expected and 1 "
+                    "was provided.",
+                    id="django_mongodb_backend.indexes.VectorSearchIndex.E006",
+                    obj=Article._meta.indexes[0],
+                ),
+            ],
+        )
+
     def test_simple(self):
         class Article(models.Model):
             vector_data = ArrayField(models.DecimalField(), size=10)