fixed index creation on default field

spec/schemas.spec.js

@@ -2939,7 +2939,7 @@ describe('schemas', () => {
             },
           },
         }).then(response => {
-          expect(response.data.indexes.name1).toEqual({ createdAt: 1 });
+          expect(response.data.indexes.name1).toEqual({ _created_at: 1 });
           done();
         });
       });

src/Adapters/Storage/Mongo/MongoStorageAdapter.js

@@ -19,6 +19,7 @@ import {
   transformWhere,
   transformUpdate,
   transformPointerString,
+  transformIndicesForSchemaUpdate as transformIndexForSchemaUpdate,
 } from './MongoTransform';
 // @flow-disable-next
 import Parse from 'parse/node';
@@ -286,9 +287,10 @@ export class MongoStorageAdapter implements StorageAdapter {
             );
           }
         });
-        existingIndexes[name] = field;
+        const transformedField = transformIndexForSchemaUpdate(className, field, {fields});
+        existingIndexes[name] = transformedField;
         insertedIndexes.push({
-          key: field,
+          key: transformedField,
           name,
         });
       }

src/Adapters/Storage/Mongo/MongoTransform.js

@@ -35,6 +35,19 @@ const transformKey = (className, fieldName, schema) => {
   return fieldName;
 };
 
+const transformIndexForSchemaUpdate = (
+  className,
+  field,
+  schema,
+) => {
+  const transformedField = {};
+  Object.keys(field).forEach((key) => {
+    const transformedKey = transformKey(className, key, schema);
+    transformedField[transformedKey] = field[key];
+  });
+  return transformedField;
+}
+
 const transformKeyValueForUpdate = (
   className,
   restKey,
@@ -1686,4 +1699,5 @@ module.exports = {
   relativeTimeToDate,
   transformConstraint,
   transformPointerString,
+  transformIndicesForSchemaUpdate: transformIndexForSchemaUpdate,
 };