How can I Aggregate and populate in mongoose

Question

I'm having problems on populating the "Main" collection, grouping works pretty well but I really don't know how to populate or even .find after aggregating. I believe I'm doing a Model casting here or so:

Main.aggregate([
      {$match : query},
      {
        $group:{
          _id: queryGroupBy,
          activated: {$sum: '$activated'},
          componentTitle: {$first:'$componentTitle'},
          titlePrefix: {$first:'$titlePrefix'},
          operator_name: {$first:'$operator_name'}
        }
      },
      {
        $project:{
          _id: '$_id',
          summation: '$activated',
          componentTitle: '$componentTitle',
          titlePrefix: '$titlePrefix',
          operator_name: '$operator_name'   
        }
      }],
      function(err,results) {
        if (err) throw err;
        result = results.map(function(doc) { 
          doc._id = doc._id,
          doc.activated = doc.activated,
          doc.componentTitle = doc.componentTitle,
          doc.titlePrefix = doc.titlePrefix,
          doc.operator_name = doc.operator_name,
          doc.fssStatusFDD = "",
          doc.dateUpdated = "",
          delete doc._id;
          delete doc.summation;

            var _main = new Main();
            _main = doc;
            console.log('test3');
            return _main
            });
        Main.populate( results, { "path": "operator_name" }, function(err,results) {
            if (err) throw err;
            console.log( JSON.stringify( results, undefined, 4 ) );
        });

        console.log('good');
        return res.send(results);
    });

Any suggestion is welcome and appreciated.

Answer 1

Found the answer seems that this will do the trick. hope this helps

    Main.aggregate([
  {$match : query},
  {
    $group:{
      _id: queryGroupBy,
      activated: {$sum: '$activated'},
      componentTitle: {$first:'$componentTitle'},
      titlePrefix: {$first:'$titlePrefix'},
      operator_name: {$first:'$operator_name'}
    }
  },
  {
    $project:{
      _id: '$_id',
      summation: '$activated',
      componentTitle: '$componentTitle',
      titlePrefix: '$titlePrefix',
      operator_name: '$operator_name'   
    }
  }],
  function(err,results) {
    Main.populate( results, { "path": "operator_name" }, function(err,results) {
        if (err) throw err;
        console.log( JSON.stringify( results, undefined, 4 ) );
        console.log('good');
        return res.send(results);
    });

});