Usando variables de ambiente

// .env, .stag.env, .prod.env

POSTGRES_DB=my_db
POSTGRES_USER=nico
POSTGRES_PASSWORD=postgres
POSTGRES_PORT=5432
POSTGRES_HOST=localhost

// src/config.ts

  
import { registerAs } from '@nestjs/config';

export default registerAs('config', () => {
  return {
    database: {
      name: process.env.DATABASE_NAME,
      port: process.env.DATABASE_PORT,
    },
    postgres: { // 👈 add config
      dbName: process.env.POSTGRES_DB,
      port: parseInt(process.env.POSTGRES_PORT, 10),
      password: process.env.POSTGRES_PASSWORD,
      user: process.env.POSTGRES_USER,
      host: process.env.POSTGRES_HOST,
    },
    apiKey: process.env.API_KEY,
  };
});

// src/database/database.module.ts

import { ConfigType } from '@nestjs/config';
import config from '../config';

@Global()
@Module({
  providers: [
    ...
    {
      provide: 'PG', 
      useFactory: (configService: ConfigType<typeof config>) => { // 👈 
        const { user, host, dbName, password, port } = configService.postgres;
        const client = new Client({
          user,
          host,
          database: dbName,
          password,
          port,
        });
        client.connect();
        return client;
      },
      inject: [config.KEY],
    },
  ],
  exports: ['API_KEY', 'PG'],
})
export class DatabaseModule {}

// src/users/services/users.service.ts
import { Client } from 'pg';

@Injectable()
export class UsersService {
  constructor(
    ...,
    @Inject('PG') private clientPg: Client, // 👈 inject PG
  ) {}

  getTasks() {
    return new Promise((resolve, reject) => {
      this.clientPg.query('SELECT * FROM tasks', (err, res) => {
        if (err) {
          reject(err);
        }
        resolve(res.rows);
      });
    });
  }
}

// src/users/controllers/users.controller.ts

@Controller('users')
export class UsersController {
  
  @Get('tasks') // 👈 new endpoint
  getTasks() {
    return this.usersService.getTasks();
  }

}