feat(ParseQuery): support using aggregate on top of constructed query

integration/test/ParseQueryAggregateTest.js

@@ -96,6 +96,25 @@ describe('Parse Aggregate Query', () => {
     expect(results[0].tempPointer.value).toEqual(2);
   });
 
+  it('aggregate pipeline on top of a simple query', async done => {
+    const pipeline = {
+      group: { objectId: '$name' },
+    };
+    let results = await new Parse.Query(TestObject)
+      .equalTo('name', 'foo')
+      .aggregate(pipeline);
+
+    expect(results.length).toBe(1);
+
+    results = await new Parse.Query(TestObject)
+      .equalTo('score', 20)
+      .aggregate(pipeline);
+
+    expect(results.length).toBe(1);
+
+    done();
+  });
+
   it('distinct query', () => {
     const query = new Parse.Query(TestObject);
     return query.distinct('score').then((results) => {

src/ParseQuery.js

@@ -781,6 +781,11 @@ class ParseQuery {
       throw new Error('Invalid pipeline must be Array or Object');
     }
 
+    if (Object.keys(this._where || {}).length) {
+      if(!Array.isArray(pipeline)) pipeline = [pipeline];
+      pipeline.unshift({ match: this._where });
+    }
+
     const params = {
       pipeline,
       hint: this._hint,