猫鼬是否提供对pre('save')中属性的先前值的访问? [英] Does Mongoose provide access to previous value of property in pre('save')?

问题描述

我想在pre('save')中间件中将属性的新/传入值与该属性的先前值(当前在db中保存的值)进行比较.

I'd like to compare the new/incoming value of a property with the previous value of that property (what is currently saved in the db) within a pre('save') middleware.

猫鼬是否提供执行此操作的功能?

Does Mongoose provide a facility for doing this?

推荐答案

猫鼬允许您配置自定义设置器来进行比较. pre('save')本身不会给您所需的东西，而是在一起:

Mongoose allows you to configure custom setters in which you do the comparison. pre('save') by itself won't give you what you need, but together:

schema.path('name').set(function (newVal) {
  var originalVal = this.name;
  if (someThing) {
    this._customState = true;
  }
});
schema.pre('save', function (next) {
  if (this._customState) {
    ...
  }
  next();
})

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