prepopulate.js

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

console.log('\n===========');
console.log('    mongoose version: %s', mongoose.version);
console.log('========\n\n');


mongoose.set('debug', true);
mongoose.connect('localhost', 'testing_prepopulate');
mongoose.connection.on('error', function () {
  console.error('connection error', arguments);
});


// user model
var userSchema = Schema({ name: 'string' });
var User = mongoose.model('User', userSchema);

// A model
var schema = new Schema({
    name: String
  , _self: { type: Schema.ObjectId, ref: 'User' }
});
schema.pre('init', function (next, doc, query) {
  // hack
  query.populate('_self');
  next();
});
var A = mongoose.model('A', schema);


mongoose.connection.on('open', function () {
  var u = new User({ name: 'mark' });
  u.save(function (err) {
    if (err) return done(err);

    var a = new A({ name: 'prepopulate', _self: u });

    a.save(function (err, a) {
      if (err) return done(err);

      A.findById(a, function (err, doc) {
        console.error('populated name "%s"', doc._self.name);
        done(err);
      });
    })
  })

});

function done (err) {
  if (err) console.error(err.stack);
  mongoose.connection.db.dropDatabase(function () {
    mongoose.connection.close();
  });
}