Where is the beest place to put prisma middleware on NestJs? - nestjs

Question

My prisma.service.ts looks like this:
#Injectable()
export class PrismaService extends PrismaClient implements OnModuleInit {
async onModuleInit() {
await this.$connect();
}
async enableShutdownHooks(app: INestApplication) {
this.$on('beforeExit', async () => {
await app.close();
});
}
}
According to Prisma docs I am supposed to put them outside the context of the request handler. That would be the app that I create on main.ts. Putting a middleware there before the app itself is defined looks wierd to me and doesn't work. I'd prefer to put it on the prisma.service.ts file itself

Answer 1

Not sure whether this is the "best" place to register them, but we do it in the constructor of the service along with the logging configuration and it works:
import { INestApplication, Injectable, Logger, OnModuleInit } from "#nestjs/common";
import { Prisma, PrismaClient } from "#prisma/client";
import { ConcurrencyErrorMiddleware } from "./concurrency-error.middleware";
#Injectable()
export class PrismaService extends PrismaClient<Prisma.PrismaClientOptions, "query"> implements OnModuleInit {
private readonly logger = new Logger(PrismaService.name);
constructor() {
super({ log: [{ emit: "event", level: "query" }] });
this.logger.log(`Prisma v${Prisma.prismaVersion.client}`);
this.$on("query", (e) => this.logger.debug(`${e.query} ${e.params}`));
this.$use(ConcurrencyErrorMiddleware());
}
async onModuleInit(): Promise<void> {
await this.$connect();
}
async enableShutdownHooks(app: INestApplication): Promise<void> {
this.$on("beforeExit", async () => {
await app.close();
});
}
}
// An example of such a middleware.
import { Prisma } from "#prisma/client";
export function ConcurrencyErrorMiddleware<T extends Prisma.BatchPayload = Prisma.BatchPayload>(): Prisma.Middleware {
return async (params: Prisma.MiddlewareParams, next: (params: Prisma.MiddlewareParams) => Promise<T>): Promise<T> => {
const result = await next(params);
if (
(params.action === "updateMany" || params.action === "deleteMany") &&
params.args.where.version &&
result.count === 0
) {
throw new ConcurrencyError();
}
return result;
};
}