Mongoose自定义虚拟字段返回承诺

const mongoose = require('mongoose');

const UserSchema = new mongoose.Schema({
  firstName: String,
  lastName: String,
});

// 自定义虚拟字段 fullName，通过计算 firstName 和 lastName 得出
UserSchema.virtual('fullName').get(function() {
  const self = this;
  return new Promise(function(resolve, reject) {
    // 模拟异步操作
    setTimeout(function() {
      const fullName = self.firstName + ' ' + self.lastName;
      resolve(fullName);
    }, 1000);
  });
});

const User = mongoose.model('User', UserSchema);

// 获取用户并打印虚拟字段 fullName
User.findById('user-id').then(function(user) {
  user.fullName.then(function(fullName) {
    console.log(fullName);
  });
});