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) There are already 10 instances of Prisma Client 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
1import { PrismaClient } from '@prisma/client'
2
3declare global {
4  // allow global `var` declarations
5  // eslint-disable-next-line no-var
6  var prisma: PrismaClient | undefined
7}
8
9export const prisma =
10  global.prisma ||
11  new PrismaClient({
12    log: ['query'],
13  })
14
15if (process.env.NODE_ENV !== 'production') global.prisma = 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 } }
}