请问：web服务器启动后连接一次数据库，就不断开了吗，一直连接吗？

连接数据库代码：

/*
 * @Descripttion: 配置 Mongodb 连接
 * @version: 1.0
 * @Author: Andy
 * @Date: 2020-01-05 11:07:21
 * @LastEditors  : Andy
 * @LastEditTime : 2020-01-05 12:05:19
 */
var mongoose = require('mongoose')
var conf = require('./conf')
var options = conf.options

/**
 * 创建 Mongo 连接池
 */
let mongoClient = mongoose.createConnection(getMongoUrl(), options)

// 连接失败回调
mongoClient.on('error', console.error.bind(console, 'connection error:'))

// 连接成功回调
mongoClient.on('connected', function () {
  console.log('Mongoose connected to ' + getMongoUrl())
})

// 关闭连接回调
mongoClient.on('disconnected', function () {
  console.log('Mongoose disconnected')
})

/**
 * @name: getMongoUrl
 * @msg: 用于拼接数据库连接的URL地址
 * @return: mongoUrl
 */
function getMongoUrl () {
  var mongoUrl = 'mongodb://'
  var username = conf.username
  var password = conf.password
  var replicaSet = conf.replicaSet
  var dbName = conf.db

  mongoUrl += `${username}:${password}@`
  // 如果配置了 replica Set 的名字则使用 seplica Set
  if (replicaSet.name) {
    var members = replicaSet.members
    for (var member of members) {
      mongoUrl += `${member.host}:${member.port},`
    }
    mongoUrl = mongoUrl.slice(0,-1) // 去掉末尾逗号
  } else {
    mongoUrl += `${conf.host}:${conf.port}`
  }
  mongoUrl += `/${dbName}`

  return mongoUrl
}

module.exports = mongoClient