1050.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.connect('localhost', 'testing_1050');
mongoose.connection.on('error', function () {
  console.error('connection error', arguments);
});

mongoose.connection.on('open', function () {
  var schema = new mongoose.Schema({
    level1: {
      level2: {}
    }
  });

  var model = mongoose.model('model', schema);
  var inst = new model();
  if (!inst.level1.level2) {
    inst.level1.level2 = {};
  }
  inst.level1.level2.dt = {
    prop1: 'value1'
  };
  console.log('Is modified -  ' + inst.isModified('level1'));
  inst.save(function(err) {
    model.findOne(function(err, rec) {
      rec.level1.level2 = {
        prop1: 'newValue2'
      };
      console.log('Is modified on a record from db -  ' + rec.isModified('level1'));
      done()
    });
  });
});

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