'this'在Mongoose预保存挂钩中未定义[重复]-'this'isundefinedinaMongoosepresavehook[duplicate]

I have made a Mongoose database schema for a User entity, and want to add the current date in an updated_at field. I am trying to use the .pre('save', function() {}) callback but every time I run it I get an error message telling me this is undefined. I've also decided to use ES6, which I guess could be a reason for this (everything works though). My Mongoose/Node ES6 code is below:

我为User实体创建了一个Mongoose数据库模式，并希望在updated_at字段中添加当前日期。我正在尝试使用.pre（'save'，function（）{}）回调，但每次运行它时都会收到一条错误消息，告诉我这是未定义的。我也决定使用ES6，我想这可能是一个原因（尽管一切正常）。我的Mongoose / Node ES6代码如下：

import mongoose from 'mongoose'

mongoose.connect("mongodb://localhost:27017/database", (err, res) => {
  if (err) {
    console.log("ERROR: " + err)
  } else {
    console.log("Connected to Mongo successfuly")
  }  
})

const userSchema = new mongoose.Schema({
  "email": { type: String, required: true, unique: true, trim: true },
  "username": { type: String, required: true, unique: true },
  "name": {
    "first": String,
    "last": String
  },
  "password": { type: String, required: true },
  "created_at": { type: Date, default: Date.now },
  "updated_at": Date
})

userSchema.pre("save", (next) => {
  const currentDate = new Date
  this.updated_at = currentDate.now
  next()
})

const user = mongoose.model("users", userSchema)
export default user

The error message is:

错误消息是：

undefined.updated_at = currentDate.now;
                       ^
TypeError: Cannot set property 'updated_at' of undefined

EDIT: Fixed this by using @vbranden's answer and changing it from a lexical function to a standard function. However, I then had an issue where, while it wasn't showing the error anymore, it wasn't updating the updated_at field in the object. I fixed this by changing this.updated_at = currentDate.now to this.updated_at = currentDate.

编辑：通过使用@ vbranden的答案并将其从词法函数更改为标准函数来解决此问题。但是，我遇到了一个问题，虽然它不再显示错误，但它没有更新对象中的updated_at字段。我通过将this.updated_at = currentDate.now更改为this.updated_at = currentDate来修复此问题。

1 个解决方案

userSchema.pre("save", (next) => {
  const currentDate = new Date
  this.updated_at = currentDate.now
  next()
})

userSchema.pre("save", function (next) {
  const currentDate = new Date
  this.updated_at = currentDate.now
  next()
})