起因
在MongoDB Node.js驱动程序中有几个弃用，Mongoose提供了解决这些弃用警告的选项
原因是因为:findOneAndUpdate()内部会使用findAndModify驱动，驱动即将被废弃，所以弹出警告！附上官方解释：Mongoose v5.5.8: Deprecation Warnings
被替换的还有下面几个：
- 将update()替换为updateOne(),updateMany(),replaceOne()
- 将remove()替换为deleteOne()或deleteMany()
- 将count()替换为countDocuments(), 除非您想要计算整个集合中有多少文档（没有过滤器）。在后一种情况下，使用estimatedDocumentCount()
报错代码
可能报错1：
(node:10256) DeprecationWarning: current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the new Server Discover and Monitoring engine, pass option { useUnifiedTopology: true } to the MongoClient constructor.
可能报错2:
(node:13604) DeprecationWarning: current URL string parser is deprecated, and will be removed in a future version. To use the new parser, pass option { useNewUrlParser: true } to MongoClient.connect.
可能报错3:
(node:5556) DeprecationWarning: Mongoose: `findOneAndUpdate()` and `findOneAndDelete()` without the `useFindAndModify` option set to false are deprecated. See: https://mongoosejs.com/docs/deprecations.html#findandmodify
此选项会影响以下模型和查询功能。没有任何故意向后突破的更改，因此您应该能够在不更改任何代码的情况下启用此选项。
Model.findByIdAndDelete()
Model.findByIdAndRemove()
Model.findByIdAndUpdate()
Model.findOneAndDelete()
Model.findOneAndRemove()
Model.findOneAndUpdate()
Query.findOneAndDelete()
Query.findOneAndRemove()
Query.findOneAndUpdate()
修复解决方案：
const mongoose = require('mongoose')
mongoose.connect(mongooseConnectStr, { useUnifiedTopology: true, useNewUrlParser: true, useFindAndModify: false }, () => console.log('MongoDB 连接成功!'))
{ useUnifiedTopology: true, useNewUrlParser: true, useFindAndModify: false } 分别对应报错顺序修复即可