Fix read preference for aggregate

spec/ReadPreferenceOption.spec.js

@@ -796,6 +796,86 @@ describe_only_db('mongo')('Read preference option', () => {
     });
   });
 
+  it('should change read preference for `aggregate` using `beforeFind`', async() => {
+    // Save objects
+    const obj0 = new Parse.Object('MyObject');
+    obj0.set('boolKey', false);
+    const obj1 = new Parse.Object('MyObject');
+    obj1.set('boolKey', true);
+    await Parse.Object.saveAll([obj0, obj1]);
+    // Add trigger
+    Parse.Cloud.beforeFind('MyObject', req => {
+      req.readPreference = 'SECONDARY';
+    });
+    // Spy on DB adapter
+    const databaseAdapter = Config.get(Parse.applicationId).database.adapter;
+    spyOn(databaseAdapter.database.serverConfig, 'startSession').and.callThrough();
+    // Query
+    const query = new Parse.Query('MyObject');
+    const results = await query.aggregate([{match:{boolKey: false}}]);
+    // Validate
+    expect(results.length).toBe(1);
+    let readPreference = null;
+    databaseAdapter.database.serverConfig.startSession.calls.all().forEach(call => {
+      if (call.args[0].owner.ns.indexOf('MyObject') > -1) {
+        readPreference = call.args[0].owner.operation.readPreference.mode;
+      }
+    });
+    expect(readPreference).toEqual(ReadPreference.SECONDARY);
+  });
+
+  it('should change read preference for `find` using query option', async() => {
+    // Save objects
+    const obj0 = new Parse.Object('MyObject');
+    obj0.set('boolKey', false);
+    const obj1 = new Parse.Object('MyObject');
+    obj1.set('boolKey', true);
+    await Parse.Object.saveAll([obj0, obj1]);
+    // Spy on DB adapter
+    const databaseAdapter = Config.get(Parse.applicationId).database.adapter;
+    spyOn(databaseAdapter.database.serverConfig, 'cursor').and.callThrough();
+    // Query
+    const query = new Parse.Query('MyObject');
+    query.equalTo('boolKey', false);
+    query.readPreference('SECONDARY');
+    const results = await query.find();
+    // Validate
+    expect(results.length).toBe(1);
+    let myObjectReadPreference = null;
+    databaseAdapter.database.serverConfig.cursor.calls.all().forEach(call => {
+      if (call.args[0].ns.collection.indexOf('MyObject') >= 0) {
+        myObjectReadPreference =
+          call.args[0].options.readPreference.mode;
+      }
+    });
+    expect(myObjectReadPreference).toEqual(ReadPreference.SECONDARY);
+  });
+
+  it('should change read preference for `aggregate` using query option', async() => {
+    // Save objects
+    const obj0 = new Parse.Object('MyObject');
+    obj0.set('boolKey', false);
+    const obj1 = new Parse.Object('MyObject');
+    obj1.set('boolKey', true);
+    await Parse.Object.saveAll([obj0, obj1]);
+    // Spy on DB adapter
+    const databaseAdapter = Config.get(Parse.applicationId).database.adapter;
+    spyOn(databaseAdapter.database.serverConfig, 'startSession').and.callThrough();
+    // Query
+    const query = new Parse.Query('MyObject');
+    query.readPreference('SECONDARY');
+    const results = await query.aggregate([{match:{boolKey: false}}]);
+    // Validate
+    expect(results.length).toBe(1);
+    let readPreference = null;
+    databaseAdapter.database.serverConfig.startSession.calls.all().forEach(call => {
+      if (call.args[0].owner.ns.indexOf('MyObject') > -1) {
+        readPreference = call.args[0].owner.operation.readPreference.mode;
+      }
+    });
+    expect(readPreference).toEqual(ReadPreference.SECONDARY);
+  });
+
   it('should find includes in same replica of readPreference by default', done => {
     const databaseAdapter = Config.get(Parse.applicationId).database.adapter;
 

src/Routers/AggregateRouter.js

@@ -54,6 +54,10 @@ export class AggregateRouter extends ClassesRouter {
       options.explain = body.explain;
       delete body.explain;
     }
+    if (body.readPreference) {
+      options.readPreference = body.readPreference;
+      delete body.readPreference;
+    }
     options.pipeline = AggregateRouter.getPipeline(body);
     if (typeof body.where === 'string') {
       body.where = JSON.parse(body.where);