使用dotenv和mongoose连接MongoDB时遇uri参数未定义错误

问题描述 #

尝试用dotenv和mongoose连接Node.js到MongoDB时，持续报错：

The 'uri' parameter to 'openUri()' must be a string, got "undefined". Make sure the first parameter to 'mongoose.connect()' or 'mongoose.createConnection()' is a string.

错误捕获中console.log(process.env.MONGO_URI)输出undefined，但类型判断显示为string，以下是涉及的代码文件：

connect.js #

const mongoose = require('mongoose')

const connectDB = (url) => {
    return mongoose.connect(url, {
        useNewUrlParser: true,
        useCreateIndex: true,
        useFindAndModify: false,
        useUnifiedTopology:true
    })
}

module.exports = connectDB

.env #

MONGO_URI = 'mongodb+srv://anousheh1:xxxxxxx@cluster0.xqrivwh.mongodb.net/?retryWrites=true&w=majority'

app.js #

const express = require('express')
const app = express()
const tasks = require('./routers/tasks')
const connectDB = require('./db/connect')
require('dotenv').config()
const find = require('./routers/.env')

// Middleware
app.use(express.json())

app.use('/api/v1/tasks', tasks)

app.get('/hello', (req, res) => {
    res.send('Task Manager App')
})


const port = 3000
const start = async () => {
    try{
        await connectDB(process.env.MONGO_URI)
        app.listen(port, console.log(`Server is listening on part ${port}`))
    } catch (error) {
        console.log(process.env.MONGO_URI)
        console.log(typeof(MONGO_URI))
        console.log(error.message)
    }
}

start()

问题分析与修复步骤 #

核心问题是process.env.MONGO_URI无法正确读取值，以下是具体错误点和修复方案：

1. 删除错误的.env文件引入 #

app.js中const find = require('./routers/.env')完全多余，且会干扰dotenv的正常加载，直接删除这行代码。

2. 修正.env文件的变量格式 #

.env文件中变量赋值不需要加单引号，且等号前后建议不要留空格，修改为：

MONGO_URI=mongodb+srv://anousheh1:xxxxxxx@cluster0.xqrivwh.mongodb.net/?retryWrites=true&w=majority

3. 修正类型判断代码 #

catch块中typeof(MONGO_URI)的写法错误，MONGO_URI不是全局变量，应改为：

console.log(typeof process.env.MONGO_URI)

4. 移除过时的Mongoose配置选项 #

Mongoose 6.x及以上版本已默认启用useNewUrlParser等选项，可简化connect.js代码：

const mongoose = require('mongoose')

const connectDB = (url) => {
    return mongoose.connect(url)
}

module.exports = connectDB

修复后完整app.js代码 #

const express = require('express')
const app = express()
const tasks = require('./routers/tasks')
const connectDB = require('./db/connect')
require('dotenv').config()

// Middleware
app.use(express.json())

app.use('/api/v1/tasks', tasks)

app.get('/hello', (req, res) => {
    res.send('Task Manager App')
})

const port = 3000
const start = async () => {
    try{
        await connectDB(process.env.MONGO_URI)
        app.listen(port, () => console.log(`Server is listening on port ${port}`))
    } catch (error) {
        console.log('MONGO_URI:', process.env.MONGO_URI)
        console.log('MONGO_URI类型:', typeof process.env.MONGO_URI)
        console.log('错误信息:', error.message)
    }
}

start()

额外检查项 #

• 确保.env文件放在项目根目录（与app.js同级），若不在根目录需给dotenv指定路径：require('dotenv').config({ path: './指定路径/.env' })
• 确认MongoDB Atlas连接字符串正确，密码无未编码的特殊字符，且已将你的IP加入Atlas白名单
• 确保安装了所有依赖：npm install express mongoose dotenv

内容的提问来源于stack exchange，提问作者anousheh21