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 globalThis
object. Then we keep a check to only instantiate PrismaClient
if it's not on the globalThis
object otherwise use the same instance again if already present to prevent instantiating extra PrismaClient
instances.
db.ts
1import { PrismaClient } from '@prisma/client'23const prismaClientSingleton = () => {4 return new PrismaClient()5}67declare global {8 var prisma: undefined | ReturnType<typeof prismaClientSingleton>9}1011const prisma = globalThis.prisma ?? prismaClientSingleton()1213export default prisma1415if (process.env.NODE_ENV !== 'production') globalThis.prisma = prisma
You can extend Prisma Client using a Prisma Client extension by appending the $extends
client method when instantiating Prisma Client as follows:
import { PrismaClient } from '@prisma/client'const prismaClientSingleton = () => {return new PrismaClient().$extends({result: {user: {fullName: {needs: { firstName: true, lastName: true },compute(user) {return `${user.firstName} ${user.lastName}`},},},},})}
After creating this file, you can now import the extended PrismaClient
instance anywhere in your Next.js pages
as follows:
// e.g. in `pages/index.tsx`import prisma from './db'export const getServerSideProps = async () => {const posts = await prisma.post.findMany()return { props: { posts } }}