猫鼬预保存钩子中未定义"this" [英] 'this' is undefined in a Mongoose pre save hook

问题描述

我为User实体制作了Mongoose数据库架构，并想在updated_at字段中添加当前日期.我正在尝试使用.pre('save', function() {})回调，但是每次运行它时，都会收到一条错误消息，告诉我this是未定义的.我还决定使用ES6，我想这可能是这样做的原因(尽管一切正常).我的Mongoose/Node ES6代码如下:

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:

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

错误消息是:

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

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，尽管它不再显示错误，但没有更新对象中的updated_at字段.我通过将this.updated_at = currentDate.now更改为this.updated_at = currentDate来解决此问题.

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.

推荐答案

问题是您的箭头函数使用词法分析此

the issue is your arrow function uses lexical this https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions

更改

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

到

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

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