Configure TypeORM by Injecting NestJS Config

NestJS comes with nice integration with TypeORM and with a nice @nestjs/config package. But getting them to work well together using dependency injection was a bit of a trick.

The docs make it look easy, and in the end it does look easy. For some reason, the docs seem incomplete and the solution not obvious. Here's one solution that worked for us.

Configure TypeORM

TypeORM is a little ORM that works well with Nest. It's configured in the app.modules.ts. One includes it in the imports like so:

import { Module } from '@nestjs/common';
import { TypeOrmModule } from '@nestjs/typeorm';

@Module({
  imports: [
    TypeOrmModule.forRoot({
      type: 'postgres',
      host: 'localhost',
      port: 5432,
      username: 'postgres',
      password: 'postgres',
      database: 'test',
    }),
  ],
})
export class AppModule {}

Values from Environment Variables

But one does not want to put static database connection strings into the committed code. Some of those things are secret or at least can change. So we want to pull them from the environment variables.

NestJS has a @nestjs/config package for that. Once it's setup, the NestJS docs taunt you with the nice usage of dependency-injected ConfigService:

const dbUser = this.configService.get<string>('DATABASE_USER');

The issue is how to get the ConfigService available to the TypeORM config that's in the AppModule decorator.

Injected ConfigService for TypeORM

Here's what worked for us, in app.module.ts:

import { Module } from '@nestjs/common';
import { ConfigModule, ConfigService } from '@nestjs/config';
import { TypeOrmModule } from '@nestjs/typeorm';

@Module({
  imports: [
    ConfigModule.forRoot({ isGlobal: true }),
    TypeOrmModule.forRootAsync({
      imports: [ConfigModule],
      inject: [ConfigService],
      useFactory: async (configService: ConfigService) => ({
        type: 'postgres' as 'postgres',
        host: configService.get('DATABASE_HOST', 'localhost'),
        port: configService.get<number>('DATABASE_PORT', 5432),
        username: configService.get('DATABASE_USER', 'postgres'),
        password: configService.get('DATABASE_PASS', 'postgres'),
        database: configService.get('DATABASE_SCHEMA', 'prism'),
      }),
    }),
  ],
})
export class AppModule {}

A few things are important here that weren't readily apparent from my naive reading of the docs:

• The type: 'postgres' as 'postgres' cast is important to specify which polymorphic type of TypeOrmModuleOptions you're returning from useFactory.
• import { ConfigService } from '@nestjs/config' is the class that you need to inject and is the type of the useFactory argument. The docs were unclear on where this was imported from or possibly custom-implemented.
• The typing of number for configService.get() and a number (5432) as fallback are important to get right as type for the port property, otherwise the TypeScript compiler is not happy with the useFactory implementation.

There are so many other examples on the web of people having to create their own ConfigService implementations. The above solution avoids that (even though we ended up going to a custom implementation later ourselves in order to share config with migrations).

Hopefully this simple solution (which we hoped against hope existed!) saves someone some time.