Support for Aggregate Queries (#4207)

* Support for Aggregate Queries

* improve pg and coverage

* Mongo 3.4 aggregates and tests

* replace _id with objectId

* improve tests for objectId

* project with group query

* typo

src/Adapters/Storage/Mongo/MongoCollection.js

@@ -60,6 +60,14 @@ export default class MongoCollection {
     return countOperation;
   }
 
+  distinct(field, query) {
+    return this._mongoCollection.distinct(field, query);
+  }
+
+  aggregate(pipeline, { maxTimeMS, readPreference } = {}) {
+    return this._mongoCollection.aggregate(pipeline, { maxTimeMS, readPreference }).toArray();
+  }
+
   insertOne(object) {
     return this._mongoCollection.insertOne(object);
   }

src/Adapters/Storage/Mongo/MongoStorageAdapter.js

@@ -405,6 +405,27 @@ export class MongoStorageAdapter {
       }));
   }
 
+  distinct(className, schema, query, fieldName) {
+    schema = convertParseSchemaToMongoSchema(schema);
+    return this._adaptiveCollection(className)
+      .then(collection => collection.distinct(fieldName, transformWhere(className, query, schema)));
+  }
+
+  aggregate(className, pipeline, readPreference) {
+    readPreference = this._parseReadPreference(readPreference);
+    return this._adaptiveCollection(className)
+      .then(collection => collection.aggregate(pipeline, { readPreference, maxTimeMS: this._maxTimeMS }))
+      .then(results => {
+        results.forEach(result => {
+          if (result.hasOwnProperty('_id')) {
+            result.objectId = result._id;
+            delete result._id;
+          }
+        });
+        return results;
+      });
+  }
+
   _parseReadPreference(readPreference) {
     if (readPreference) {
       switch (readPreference) {