在Mongoose中处理初始不存在的字段

const userSchema = new mongoose.Schema({
  age: {
    type: Number,
    default: 18 // 设置默认值为18
  }
});

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

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

userSchema.virtual('fullName').get(function() {
  return this.firstName + ' ' + this.lastName;
});

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