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

CHANGELOG.md

@@ -104,6 +104,7 @@ ___
 - Add REST API endpoint `/loginAs` to create session of any user with master key; allows to impersonate another user. (GormanFletcher) [#7406](https://github.com/parse-community/parse-server/pull/7406)
 
 ### Other Changes
+- Support aggregation stage names starting with `$` and `$group` stages using `_id` instead of `objectId`, just like in MongoDB (Raschid JF Rafeally) [#7339](https://github.com/parse-community/parse-server/pull/7339)
 - Fix error when a not yet inserted job is updated (Antonio Davi Macedo Coelho de Castro) [#7196](https://github.com/parse-community/parse-server/pull/7196)
 - request.context for afterFind triggers (dblythy) [#7078](https://github.com/parse-community/parse-server/pull/7078)
 - Winston Logger interpolating stdout to console (dplewis) [#7114](https://github.com/parse-community/parse-server/pull/7114)

spec/AggregateRouter.spec.js

@@ -85,4 +85,22 @@ describe('AggregateRouter', () => {
     const result = AggregateRouter.getPipeline(body);
     expect(result).toEqual(expected);
   });
+
+  it("support stage name starting with '$'", () => {
+    const body = {
+      $match: { someKey: 'whatever' },
+    };
+    const expected = [{ $match: { someKey: 'whatever' } }];
+    const result = AggregateRouter.getPipeline(body);
+    expect(result).toEqual(expected);
+  });
+
+  it("support group stage using '_id'", () => {
+    const body = {
+      group: { _id: {} },
+    };
+    const expected = [{ $group: { _id: {} } }];
+    const result = AggregateRouter.getPipeline(body);
+    expect(result).toEqual(expected);
+  });
 });

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')) {
-        throw new Parse.Error(
-          Parse.Error.INVALID_QUERY,
-          `Invalid parameter for query: group. Please use objectId instead of _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], 'objectId')) {
+      if (!Object.prototype.hasOwnProperty.call(stage[stageName], '_id')) {
         throw new Parse.Error(
           Parse.Error.INVALID_QUERY,
-          `Invalid parameter for query: group. objectId is required`
+          `Invalid parameter for query: group. Missing key _id`
         );
       }
-      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() {