How can I run the code only once when Next.js starts, instead of once for each request?

Question

I am a beginner in Next.js and I want to use mongoose in Next.js, but I don't know where to connect to the database. When I use Mongoose in Express, I connect to the database in app.js, so MongoDB only connects once at startup.

// app.js
const express = require('express');
const mongoose = require("mongoose");
const userRouter = require('./routes/user_actions');
const app = express();

// Connect to MongoDB; this code will only run once when the app starts.
await mongoose.connect('mongodb://localhost:27017/user');

app.use('/user', userRouter);
module.exports = app;

But in Next.js, I don't know where to connect to the database. I connect to the database in the app/route.js, but every request will connect to the database, which is not what I want. I wonder if it's possible to run the code once at startup in Next.js, like Express, instead of running the code once every time a request is made.

// app/route.js
import {NextResponse} from 'next/server'
import mongoose from 'mongoose'

// Connect to MongoDB; this code will run on every request.
mongoose.connect('mongodb://localhost:27017/user')

export async function POST(request: Request) {
    const res = await request.json()
    console.log(request);
    console.log(res);
    return NextResponse.json({hello: 'world'})
}

I noticed a similar question here, but there is no answer.

What should I do in Next.js?

Thanks.

Answer 1

Use mongoose.connection.readyState.

return:

• 0 = disconnected
• 1 = connected
• 2 = connecting
• 3 = disconnecting
• 99 = uninitialized

if (mongoose.connection.readyState === 1) {
    console.log("is already connected");
    return;
}
mongoose.connect('mongodb://localhost:27017/user');