Exemplo de DBRef

Busca.js

Host.findOne({nome: req.body.host})
    .populate('dominio')
    .exec(function (err, host) {
         console.log(host);
         
});

Dominio.js

'use strict';

var mongoose = require('mongoose'),
    Schema = mongoose.Schema;

var Dominio = new Schema({
  _id: { type: Schema.ObjectId },
  nome: { type: String, default: '' },
  ipAddress: { type: String },
  hmac: { type: String },
  ativo: { type: String },

});
module.exports = mongoose.model('Dominio', Dominio);

dominio.json

{
    "_id" : ObjectId("539f82200ace836f35c52f2c"),
    "nome" : "dtux.org",
    "ipAddress" : "192.168.0.1",
    "hmac" : "Kdiego.org.+157+14340.private",
    "alteracoes" : 1,
    "ativo" : true,
    "criadoEm" : ISODate("2014-06-16T20:47:44.369-03:00"),
    "atualizadoEm" : ISODate("2014-06-16T20:47:50.081-03:00")
}

Host.js

'use strict';

var mongoose = require('mongoose'),
    Schema = mongoose.Schema;
var Dominio = require('./Dominio');

var Host = new Schema({
  nome: { type: String, default: '' },
  ativo: { type: String, default: '' },
  ipAddress: { type: String, default: '' },
  dominio: { type : Schema.ObjectId, ref : 'Dominio' }
}, { collection: 'Host' });

module.exports = mongoose.model('Host', Host);

host.json

{
    "_id" : ObjectId("539f82200ace836f35c52f39"),
    "nome" : "pc5",
    "ip_address" : "6b1328a2d1d06b1be5ca1078e6e8810d2550b48e",
    "ipAddress" : "192.168.0.5",
    "dominio" : {
        "$ref" : "Dominio",
        "$id" : ObjectId("539f82200ace836f35c52f2c"),
        "$db" : "simpleDDNS"
    },
    "alteracoes" : 0,
    "ativo" : true,
    "criadoEm" : ISODate("2014-06-16T20:47:44.379-03:00"),
    "atualizadoEm" : ISODate("2014-06-16T20:47:44.379-03:00")
}