Best practice for instantiating PrismaClient with Next.js

Problem

Lots of users have come across this warning while working with Next.js in development:

warn(prisma-client) Already 10 Prisma Clients are actively running

There's a related discussion and issue for the same.

In development, the command next dev clears Node.js cache on run. This in turn initializes a new PrismaClient instance each time due to hot reloading that creates a connection to the database. This can quickly exhaust the database connections as each PrismaClient instance holds its own connection pool.

Solution

The solution in this case is to instantiate a single instance PrismaClient and save it on the global object. Then we keep a check to only instantiate PrismaClient if it's not on the global object otherwise use the same instance again if already present to prevent instantiating extra PrismaClient instances.

// db.ts
import { PrismaClient } from '@prisma/client'
declare global {
var prisma: PrismaClient
}
let prisma: PrismaClient
// check to use this workaround only in development and not in production
if (process.env.NODE_ENV === 'production') {
prisma = new PrismaClient()
} else {
if (!global.prisma) {
global.prisma = new PrismaClient()
}
prisma = global.prisma
}
export default prisma

After creating this file, you can now import this PrismaClient instance anywhere in your Next.js pages as follows:

// e.g. in `pages/index.tsx`
import prisma from './db'
export const getServerSideProps = async ({ req }) => {
const token = req.headers.AUTHORIZATION
const userId = await getUserId(token)
const posts = await prisma.post.findMany({
where: {
author: { id: userId },
},
})
return { props: { posts } }
}
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