feat(AggregateRouter): support native mongodb syntax in aggregation pipelines (#7339)

src/Routers/AggregateRouter.js

@@ -3,6 +3,7 @@ import rest from '../rest';
 import * as middleware from '../middlewares';
 import Parse from 'parse/node';
 import UsersRouter from './UsersRouter';
+import Deprecator from '../Deprecator/Deprecator';
 
 export class AggregateRouter extends ClassesRouter {
   handleFind(req) {
@@ -91,22 +92,30 @@ export class AggregateRouter extends ClassesRouter {
 
   static transformStage(stageName, stage) {
     if (stageName === 'group') {
-      if (Object.prototype.hasOwnProperty.call(stage[stageName], '_id')) {
+      if (Object.prototype.hasOwnProperty.call(stage[stageName], 'objectId')) {
+        Deprecator.logRuntimeDeprecation({
+          usage: 'The use of objectId in aggregation stage $group',
+          solution: 'Use _id instead.',
+        });
+        stage[stageName]._id = stage[stageName].objectId;
+        delete stage[stageName].objectId;
+      }
+      if (!Object.prototype.hasOwnProperty.call(stage[stageName], '_id')) {
         throw new Parse.Error(
           Parse.Error.INVALID_QUERY,
-          `Invalid parameter for query: group. Please use objectId instead of _id`
+          `Invalid parameter for query: group. Missing key _id`
         );
       }
-      if (!Object.prototype.hasOwnProperty.call(stage[stageName], 'objectId')) {
-        throw new Parse.Error(
-          Parse.Error.INVALID_QUERY,
-          `Invalid parameter for query: group. objectId is required`
-        );
-      }
-      stage[stageName]._id = stage[stageName].objectId;
-      delete stage[stageName].objectId;
     }
-    return { [`$${stageName}`]: stage[stageName] };
+
+    if (stageName[0] !== '$') {
+      Deprecator.logRuntimeDeprecation({
+        usage: "Using aggregation stages without a leading '$'",
+        solution: `Try $${stageName} instead.`,
+      });
+    }
+    const key = stageName[0] === '$' ? stageName : `$${stageName}`;
+    return { [key]: stage[stageName] };
   }
 
   mountRoutes() {