how to use populate and aggregate in same statement?

this is my appointment collection

{ _id: ObjectId("518ee0bc9be1909012000002"), date: ISODate("2013-05-13T22:00:00Z"), patient:ObjectId("518ee0bc9be1909012000002") }

{ _id: ObjectId("518ee0bc9be1909012000002"), date: ISODate("2013-05-13T22:00:00Z"), patient:ObjectId("518ee0bc9be1909012000002") }

{ _id: ObjectId("518ee0bc9be1909012000002"), date: ISODate("2013-05-13T22:00:00Z"), patient:ObjectId("518ee0bc9be1909012000002") }

i use aggregate to get result like this

{date: ISODate("2013-05-13T22:00:00Z"),
patients:[ObjectId("518ee0bc9be1909012000002"),ObjectId("518ee0bc9be1909012000002"),ObjectId("518ee0bc9be1909012000002")] }

like this

Appointments.aggregate([
{$group: {_id: '$date', patients: {$push: '$patient'}}},
{$project: {date: '$_id', patients: 1, _id: 0}}
], ...)

how can populate patient document i try this but not work ... Appointments.find({}).populate("patient").aggregate....

in other word can use populate and aggregate in same statement

any help please

With the latest version of mongoose (mongoose >= 3.6), you can but it requires a second query, and using populate differently. After your aggregation, do this:

Patients.populate(result, {path: "patient"}, callback);

See more at the Mongoose API and the Mongoose docs.

Short answer: You can't.

Long answer: In the Aggregation Framework, the returned fields are built by you, and you're able to "rename" document properties.

What this means is that Mongoose can't identify that your referenced documents will be available in the final result.

The best thing you can do in such a situation is populate the field you want after the query has returned. Yes, that would result in two DB calls, but it's what MongoDB allows us to do.

Somewhat like this:

Appointments.aggregate([ ... ], function( e, result ) {
  if ( e ) return;

  // You would probably have to do some loop here, as probably 'result' is array
  Patients.findOneById( result.patient, function( e, patient ) {
    if ( e ) return;

    result.patient = patient;
  });
});