使用mongoose递增子文档密钥

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

const childSchema = new Schema({
  key: {
    type: Schema.Types.ObjectId,
    default: function() {
      return new mongoose.Types.ObjectId();
    }
  },
  // 其他子文档字段
});

const parentSchema = new Schema({
  children: [childSchema],
  // 其他父文档字段
});

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

// 创建父文档
const parent = new ParentModel();

// 添加子文档
parent.children.push({});

// 访问子文档的密钥字段
console.log(parent.children[0].key);