Prisma•4mo ago

Get type of prisma client before it is defined

In my next.js app I have to use the following approach to prevent multiple instances of PrismaClient being created

import { PrismaClient } from "@prisma/client";

const extension = {
  model: {
    user: {
        example: () => "example",
      },
  },
};

const globalForPrisma = globalThis as unknown as { db: PrismaClient };
const db = globalForPrisma.db || new PrismaClient().$extends(extension);

export default db;

if (process.env.NODE_ENV !== "production") globalForPrisma.db = db;

import { PrismaClient } from "@prisma/client";

const extension = {
  model: {
    user: {
        example: () => "example",
      },
  },
};

const globalForPrisma = globalThis as unknown as { db: PrismaClient };
const db = globalForPrisma.db || new PrismaClient().$extends(extension);

export default db;

if (process.env.NODE_ENV !== "production") globalForPrisma.db = db;

The above approach however is problematic because it doesn't generate the correct PrismaClient type. E.g. in my project TS will complain that db.user.example doesn't exist. I tried solving this with typeof new PrismaClient().$extends(extension) but I need globalForPrisma to be defined before the PrismaClient has been defined

10 Replies

ncls.•4mo ago

I use the following solution in a file called prisma.ts where I then import my client from:

import { PrismaClient } from '@prisma/client';

declare global {
  var prisma: PrismaClient | undefined;
}

const prisma = globalThis.prisma || new PrismaClient();

if (process.env.NODE_ENV !== 'production') globalThis.prisma = prisma;

export default prisma;

import { PrismaClient } from '@prisma/client';

declare global {
  var prisma: PrismaClient | undefined;
}

const prisma = globalThis.prisma || new PrismaClient();

if (process.env.NODE_ENV !== 'production') globalThis.prisma = prisma;

export default prisma;

Nikita Revenco•4mo ago

Thank you! I found an alternative solution without having to use declarations (someone told me they're unsafe).

const extension = {/*...*/}
const createPrismaClient = () => {
  return new PrismaClient().$extends(extension);
};

const globalForPrisma = globalThis as unknown as {
  db: ReturnType<typeof createPrismaClient>;
};
const db = globalForPrisma.db || createPrismaClient();

const extension = {/*...*/}
const createPrismaClient = () => {
  return new PrismaClient().$extends(extension);
};

const globalForPrisma = globalThis as unknown as {
  db: ReturnType<typeof createPrismaClient>;
};
const db = globalForPrisma.db || createPrismaClient();

Nikita Revenco•4mo ago

I am getting this error though

ncls.•4mo ago

Are you trying to run prisma in the middleware? That doesn't work since the middlware is run on the edge runtime which Prisma can't do

Nikita Revenco•4mo ago

This isn't on the middleware, it's in prisma/index.ts. This error doesn't happen if I remove the createPrismaClient function. e.g.: No Error:

const globalForPrisma = globalThis as unknown as {
  db: PrismaClient;
};

const db = globalForPrisma.db || new PrismaClient();

const globalForPrisma = globalThis as unknown as {
  db: PrismaClient;
};

const db = globalForPrisma.db || new PrismaClient();

Yes Error:

const createPrismaClient = () => {
  return new PrismaClient().$extends(extension);
};

const globalForPrisma = globalThis as unknown as {
  db: ReturnType<typeof createPrismaClient>;
};

const db = globalForPrisma.db || createPrismaClient()

const createPrismaClient = () => {
  return new PrismaClient().$extends(extension);
};

const globalForPrisma = globalThis as unknown as {
  db: ReturnType<typeof createPrismaClient>;
};

const db = globalForPrisma.db || createPrismaClient()

ncls.•4mo ago

Then try my code. I don't know why it would be unsafe to use it.

Nikita Revenco•4mo ago

Your code has the same problem as mine though, since you are setting prisma: PrismaClient if you want your prisma client to have an extension it will be of the wrong type. eg:

import { PrismaClient } from '@prisma/client';

const extension = { /* ... */ }

declare global {
  var prisma: PrismaClient | undefined;
}

const prisma = globalThis.prisma || new PrismaClient().$extends(extension);

if (process.env.NODE_ENV !== 'production') globalThis.prisma = prisma;

export default prisma;

import { PrismaClient } from '@prisma/client';

const extension = { /* ... */ }

declare global {
  var prisma: PrismaClient | undefined;
}

const prisma = globalThis.prisma || new PrismaClient().$extends(extension);

if (process.env.NODE_ENV !== 'production') globalThis.prisma = prisma;

export default prisma;

You see, we have added an extension to PrismaClient but the type of prisma is still PrismaClient, so like if our extension has a method then typescript won't know about it Ideally we can somehow set var prisma: PrismaClientWithExtension<typeof extension> or something like that. Not sure if it's a thing though

ncls.•4mo ago

You can create a type which has all the additional typing and then do

type PrismaClientWithExtension = PrismaClient & {
  // All your additional attributes...
}

declare global {
  var prisma: PrismaClientWithExtension | undefined;
}

type PrismaClientWithExtension = PrismaClient & {
  // All your additional attributes...
}

declare global {
  var prisma: PrismaClientWithExtension | undefined;
}

Nikita Revenco•4mo ago

That's a cool idea but I tried it and it doesn't work unfortunately. My extension is like this:

const extension = {
  model: {
    user: {
      example: () => {},
    },
  },
};

const extension = {
  model: {
    user: {
      example: () => {},
    },
  },
};

Nikita Revenco•4mo ago

What actually happens is TS thinks that db has db.model which shouldn't happen

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Get type of prisma client before it is defined