如何在mongoose中添加孩子(Ref)？

const mongoose = require('mongoose');

const parentSchema = new mongoose.Schema({
  name: String,
  children: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Child' }]
});

const childSchema = new mongoose.Schema({
  name: String
});

const Parent = mongoose.model('Parent', parentSchema);
const Child = mongoose.model('Child', childSchema);

const parent = new Parent({ name: 'Parent 1' });
const child = new Child({ name: 'Child 1' });

child.save(function(err) {
  if (err) throw err;

  parent.children.push(child);
  parent.save(function(err) {
    if (err) throw err;
    console.log('Child added to parent successfully.');
  });
});