Javascript 使用mongoose查找后如何更改子文档

我有一些类似下面使用mongoose的代码

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

mongoose.connect('mongodb://localhost/hoge');
var UserSchema = new Schema({
  name: String,
  children: [ChildSchema],
});
var ChildSchema = new Schema({
  name: String,
}, {_id: false});

var User = mongoose.model('User', UserSchema);
var Child = mongoose.model('Child', ChildSchema);

User.findOne({_id: '52299322fdbbdec515000001'}, function(err, user) {
  console.log(user);
  for (var i=0; i<user.children.length; i++) {
    var child = user.children[i];
    child.name = 'newchild';
  }
  user.save(function(err) {
    console.log(user);
    mongoose.disconnect();
  });
});

当我运行脚本时，它会在下面输出

{ name: 'u1',
  _id: 52299322fdbbdec515000001,
  __v: 0,
  children: [ { name: 'c2' } ] }

{ name: 'u1',
  _id: 52299322fdbbdec515000001,
  __v: 0,
  children: [ { name: 'newchild' } ] }

但我在mongodb的记录没有改变。为什么?

仅供参考，如果我在保存前插入此代码，记录将更改

user.children.push({name: 'somechild'});

---

对不起，我已经决定了

问题在于声明模式的顺序

如果我尝试这个改变，它会起作用

/* first, children's schema */
var ChildSchema = new Schema({
  name: String,
}, {_id: false});

/* seconds, parent's schema */
var UserSchema = new Schema({
  name: String,
  children: [ChildSchema],
});

/* first, children's schema */
var ChildSchema = new Schema({
  name: String,
}, {_id: false});

/* seconds, parent's schema */
var UserSchema = new Schema({
  name: String,
  children: [ChildSchema],
});