How to populate after mapReduce?

[Burak Kilic]

Hi;

I am trying to populate reference fields after mapReduce:

 var o = {};  

  o.query = { 'place' : req.param('place') ,

              '_id' : {'$nin':req.user.ratings}

            }

  o.map = function () { emit(0, {k: this, v: Math.random()})  }

  o.reduce = function(k, v) {

    var a = []

    v.forEach(function(x) {

      a = a.concat(x.a ? x.a : x)

    })

    return {a:a.sort(function(a, b) {

      return a.v - b.v;

    }).slice(0, 10 /*how many records you want*/)}; 

  }

  o.finalize = function(k, v) {

    return v.a.map(function(x) {

      return x.k

    })

  }

  o.out = { replace: 'createdCollectionNameForResults' };

  Venue.mapReduce(o, function (err, results) {

    mongoose.connection.db.collection('createdCollectionNameForResults', function(err, collection) { //query the new map-reduced table

        collection.find({}).populate('place').toArray(function(err, pings) { //only pull in the top 10 results and sort descending by number of pings

               res.send(200, pings)

        });

    });

  })

But I am getting TypeError because collection.find({}) is from MongoDB, not from Mongoose. How can I populate references?

[Aaron Heckmann]

In 3.x you receive a model back from mapReduce you can query the result collection with but it doesn't permit population:

Venue.mapReduce(o, function (err, model) {

  model.find(..).exec(function (err, docs) {

    // perform manual population here

    // docs are plain js objects, not mongoose documents

  })

})

http://mongoosejs.com/docs/api.html#model_Model.mapReduce

http://mongoosejs.com/docs/api.html#query_Query-populate

However, in 3.6 you will be able to populate.

Venue.mapReduce(o, function (err, model) {

  model.find(..).populate({ path: 'some.place', model: 'Place' }).exec(err, pings) {

    console.log(pings)

  })

})

In fact, in 3.6 you'll be able to populate any ad-hoc property you wish as long as you specify the model name.

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@aaronheckmann