next.js/examples/with-mysql/lib/prisma.ts

import { PrismaPlanetScale } from "@prisma/adapter-planetscale";
import { PrismaClient } from "./generated/prisma/client";
import { fetch as undiciFetch } from "undici";

const globalForPrisma = globalThis as unknown as {
  prisma: PrismaClient | undefined;
};

function createPrismaClient() {
  const adapter = new PrismaPlanetScale({
    url: process.env.DATABASE_URL,
    fetch: undiciFetch,
  });
  return new PrismaClient({ adapter });
}

const prisma = globalForPrisma.prisma ?? createPrismaClient();

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

export default prisma;