Mongoose populate nested array

Question

Assuming the following 3 models:

var CarSchema = new Schema({   name: {type: String},   partIds: [{type: Schema.Types.ObjectId, ref: 'Part'}], });  var PartSchema = new Schema({   name: {type: String},   otherIds: [{type: Schema.Types.ObjectId, ref: 'Other'}], });  var OtherSchema = new Schema({   name: {type: String} }); 

When I query for Cars I can populate the parts:

Car.find().populate('partIds').exec(function(err, cars) {   // list of cars with partIds populated }); 

Is there a way in mongoose to populate the otherIds in the nested parts objects for all the cars.

Car.find().populate('partIds').exec(function(err, cars) {   // list of cars with partIds populated   // Try an populate nested   Part.populate(cars, {path: 'partIds.otherIds'}, function(err, cars) {     // This does not populate all the otherIds within each part for each car   }); }); 

I can probably iterate over each car and try to populate:

Car.find().populate('partIds').exec(function(err, cars) {   // list of cars with partIds populated    // Iterate all cars   cars.forEach(function(car) {      Part.populate(car, {path: 'partIds.otherIds'}, function(err, cars) {        // This does not populate all the otherIds within each part for each car      });   }); }); 

Problem there is that I have to use a lib like async to make the populate call for each and wait until all are done and then return.

Possible to do without looping over all cars?

Answer 1

Update: Please see Trinh Hoang Nhu's answer for a more compact version that was added in Mongoose 4. Summarized below:

Car   .find()   .populate({     path: 'partIds',     model: 'Part',     populate: {       path: 'otherIds',       model: 'Other'     }   }) 

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Mongoose 3 and below:

Car   .find()   .populate('partIds')   .exec(function(err, docs) {     if(err) return callback(err);     Car.populate(docs, {       path: 'partIds.otherIds',       model: 'Other'     },     function(err, cars) {       if(err) return callback(err);       console.log(cars); // This object should now be populated accordingly.     });   }); 

For nested populations like this, you have to tell mongoose the Schema you want to populate from.

Answer 2

Mongoose 4 support this

Car .find() .populate({   path: 'partIds',   model: 'Part',   populate: {     path: 'otherIds',     model: 'Other'   } })