In a Mongoose Schema return "parent" collection specific value

I believe that you're very close. Your question isn't very clear on this, but I assume that

.populate('_ipset', ['name']).exec(function (error, doc) {  console.log(doc._ipset.name);});

is working and

.populate('_ipset', ['name']).exec(function (error, doc) {   return doc._ipset.name;});

is not?

Unfortunately the async return is not working the way you want it to.

.exec calls your callback function, which returns the name. This does not return the name as the return value for get_parent_name(), though. That would be nice. (Imagine the return return name syntax.)

Pass in a callback into get_parent_name() like this:

Hash_IP.methods.get_parent_name = function get_parent_name(callback) {    this.model('Hash_IP').findOne({ _ipset: this._ipset })        .populate('_ipset', ['name'])        .exec(callback);};

You can now use instance_of_hash_ip.get_parent_name(function (err, doc) { ... do something with the doc._ipset.name ... }); in your code.

Bonus answer ;)

If you use your parent's name a lot, you might want to always return it with your initial query. If you put the .populate(_ipset, ['name']) into your query for the instance of Hash_IP, then you won't have to deal with two layers of callbacks in your code.

Simply put the find() or findOne(), followed by populate() into a nice static method of your model.

Bonus example of bonus answer :)

var Hash_IP = new Schema({    _ipset      : {        type: ObjectId,        ref: 'IP_Set'    },    description : String});Hash_IP.statics.findByDescWithIPSetName = function (desc, callback) {    return this.where('description', new RegExp(desc, 'i'))        .populate('_ipset', ['name']) //Magic built in        .exec(cb)};module.exports = HashIpModel = mongoose.model('HashIp', Hash_IP);// Now you can use this static method anywhere to find a model // and have the name populated already:HashIp = mongoose.model('HashIp'); //or require the model you've exported aboveHashIp.findByDescWithIPSetName('some keyword', function(err, models) {   res.locals.hashIps = models; //models is an array, available in your templates});

Each model instance now has models._ipset.name already defined. Enjoy :)