fix(api): support enums in query predicates for model helpers (#1595)

Author: Travis Sheppard

packages/api/amplify_api/lib/src/graphql/graphql_request_factory.dart

@@ -341,7 +341,8 @@ String _getGraphQLFilterExpression(QueryFieldOperatorType operatorType) {
   return result;
 }
 
-/// Convert Temporal* and DateTime values to string if needed; otherwise return unchanged.
+/// Convert Temporal*, DateTime and enum values to string if needed.
+/// Otherwise return unchanged.
 dynamic _getSerializedValue(dynamic value) {
   if (value is TemporalDateTime ||
       value is TemporalDate ||
@@ -352,5 +353,8 @@ dynamic _getSerializedValue(dynamic value) {
   if (value is DateTime) {
     return _getSerializedValue(TemporalDateTime(value));
   }
+  if (value is Enum) {
+    return describeEnum(value);
+  }
   return value;
 }

packages/api/amplify_api/test/query_predicate_graphql_filter_test.dart

@@ -2,8 +2,11 @@ import 'package:amplify_api/amplify_api.dart';
 import 'package:amplify_api/src/graphql/graphql_request_factory.dart';
 import 'package:amplify_core/amplify_core.dart';
 import 'package:amplify_test/test_models/ModelProvider.dart';
+import 'package:flutter/foundation.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+enum Size { SMALL, MEDIUM, LARGE }
+
 void main() {
   group('queryPredicateToGraphQLFilter()', () {
     // needed to fetch the schema from within the helper
@@ -209,5 +212,17 @@ void main() {
       _testQueryPredicateTranslation(queryPredicate, expectedFilter,
           modelType: Post.classType);
     });
+
+    test('query with enum should serialize to string', () {
+      // Note: enums are not actually in the codegen model. Nonetheless, we
+      // expect this predicate to translate as follows.
+      final queryPredicate = Post.TITLE.eq(Size.MEDIUM);
+      final expectedFilter = {
+        'title': {'eq': describeEnum(Size.MEDIUM)}
+      };
+
+      _testQueryPredicateTranslation(queryPredicate, expectedFilter,
+          modelType: Post.classType);
+    });
   });
 }