The Singleton Pattern for Database Connections

Snippet

The Singleton Pattern for Database Connections

In development, Next.js frequently reloads modules. Without the Singleton pattern, every hot-reload would create a new database connection, eventually exhausting the pool. This pattern stores the instance globally.

snippet.js
javascript
import { PrismaClient } from '@prisma/client';
 
const prismaClientSingleton = () => new PrismaClient();
 
const globalForPrisma = globalThis as unknown as {
  prisma: PrismaClient | undefined;
};
 
const prisma = globalForPrisma.prisma ??= prismaClientSingleton();
 
export default prisma;
 
if (process.env.NODE_ENV !== 'production') globalForPrisma.prisma = prisma;

nextjs

Breakdown

globalThis

A standard way to access the global scope across different environments (Node.js/Browser).

??=

The logical nullish assignment operator, which only assigns if the variable is null or undefined.

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The Singleton Pattern for Database Connections

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