在连接MongoDB数据库时，去除Node中提示的碍眼东西

在连接MongoDB数据库时，去除Node中提示的碍眼东西：

第一个：

(node) 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.

第二个：

(node) 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.

第三个：

(node) DeprecationWarning: collection.ensureIndex is deprecated. Use createIndexes

解决方法：

// 引入mongoose第三方模块
const mongoose = require('mongoose');
// 连接数据库
mongoose.set('useCreateIndex', true) ;//解决第三个
mongoose.connect('mongodb://localhost/blog', {useNewUrlParser: true ,useUnifiedTopology: true})//解决第一个和第二个
	.then(() => console.log('数据库连接成功'))
	.catch(() => console.log('数据库连接失败'));