How to create a custom health check for Prisma with #nestjs/terminus? - nestjs

Question

Since #nestjs/terminus doesn't provide a health check for Prisma, I'm trying to create it based on their Mongoose health check.
When I try:
import * as Prisma from 'prisma';
...
...
private getContextConnection(): any | null {
const {
getConnectionToken,
// eslint-disable-next-line #typescript-eslint/no-var-requires
} = require('prisma') as typeof Prisma;
try {
return this.moduleRef.get(getConnectionToken('DatabaseConnection') as string, {
strict: false,
});
} catch (err) {
return null;
}
}
...
...
const connection = options.connection || this.getContextConnection();
if (!connection) {
throw new ConnectionNotFoundError(
this.getStatus(key, isHealthy, {
message: 'Connection provider not found in application context',
}),
);
}
I always seem to get: "message": "Connection provider not found in application context".
There is a problem with the connection or I don't really understand how the health check actually works

Answer 1

This question helped me build a Prisma health check for NestJS.
Here's what I made:
import { Injectable } from "#nestjs/common";
import { HealthCheckError, HealthIndicator, HealthIndicatorResult } from "#nestjs/terminus";
import { PrismaService } from "./prisma.service";
#Injectable()
export class PrismaHealthIndicator extends HealthIndicator {
constructor(private readonly prismaService: PrismaService) {
super();
}
async isHealthy(key: string): Promise<HealthIndicatorResult> {
try {
await this.prismaService.$queryRaw`SELECT 1`;
return this.getStatus(key, true);
} catch (e) {
throw new HealthCheckError("Prisma check failed", e);
}
}
}
This injects a PrismaService exactly as it is shown in the NestJS docs. https://docs.nestjs.com/recipes/prisma#use-prisma-client-in-your-nestjs-services
You could alternatively replace prismaService with new PrismaClient().

Answer 2

A naive copy of the mongoose implementation isn't going to work because there are differences between the NestJSMongoose type/module and Prisma. In particular, getConnectionToken does not exist inside the Prisma package.
I can't comment on what the best way would be to extend terminus to support prisma. You might have to dig a bit into the terminus interface for that. However, a simple way to get a health check/ping in Prisma is to use the following query:
prisma.$queryRaw`SELECT 1`