我只想通过猫鼬将我的数据库连接到我的本地主机上。但是，我收到此错误：

C:\Users\przyb\Desktop\JWT\node_modules\mongoose\lib\connection.js:520
    throw new MongooseError('The `uri` parameter to `openUri()` must be a ' +
    ^
MongooseError: 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.

这让我感到困惑，因为要传递的变量肯定是字符串。这是我的文件树：

JWT
|
model --- User.js
node_modules
public
routes --- .env.js,auth.js
views
index.js
package.json
package-lock.json

index.js

const express = require("express");
const app = express();
const mongoose = require("mongoose");
const dotenv = require("dotenv").config();

//Imported routes
const authRoute = require('./routes/auth');

//Connect to db
mongoose.connect(
    process.env.DB_CONNECT,{useNewUrlParser:true},() => console.log("connected to db")
);

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

//Route Middlewares
app.use('/api/User',authRoute);

app.listen(3000,() => console.log("All good"));

.env.js

DB_CONNECT = "mongodb+srv://username:PASSWORD@cluster0-wu2im.mongodb.net/test?retryWrites=true&w=majority";

Stackoverflow表示我对此问题的代码过多，因此无法向您展示auth.js和User.js。