Best nestjs config approach

readme.md

• Can be used without DI - just instantiate
• You get types - no explicit type imports etc
• You can define computed fields etc
• You can refactor ENV names without affecting the service fields :)
• You can structure and nest the fileds however you want
• Super simple to reason about & maintain - no need to rely on magic

config.module.ts

import { Global, Module } from '@nestjs/common';

import { ConfigService } from './config.service';

@Global()
@Module({
  providers: [ConfigService],
  exports: [ConfigService],
})
export class ConfigModule {}

config.options.ts

import {
  IsBoolean,
  IsEnum,
  IsNotEmpty,
  IsNumber,
  IsOptional,
} from 'class-validator';

export class ConfigOptions {
  //mind boolean casting with class-transformer - use decorator @ToBoolean
  @IsBoolean()
  @IsOptional()
  DEBUG?: boolean = false;

  @IsNotEmpty()
  POSTGRES_HOST: string;

  @IsNotEmpty()
  POSTGRES_USERNAME: string;

  @IsNotEmpty()
  POSTGRES_PASSWORD: string;

  @IsNotEmpty()
  REDIS_HOST: string;
}

config.service.ts

import { Injectable } from '@nestjs/common';
import { plainToClass } from 'class-transformer';
import { validateSync } from 'class-validator';
import * as dotenv from 'dotenv';

import { ConfigOptions } from './config.options';

//sets to process.env what we have in .env
dotenv.config();

/**
 * @description
 * - Can be used without DI - just instantiate
 * - You get types - no explicit type imports etc
 * - You should expose getter for each field you want
 * - You can define computed fields etc, but everything
 * - You can refactor ENV names without affecting the service fields :)
 *   which this service exposes should be read only
 * - prefer grouping fields with same prefix - makes things more readable
 * @export
 * @class ConfigService
 */
@Injectable()
export class ConfigService {
  private readonly env: ConfigOptions;

  constructor() {
    const transformed = plainToClass(ConfigOptions, process.env);

    const errors = validateSync(transformed, {
      /**
       * Will strip not declared with decorator in options fields
       */
      whitelist: true,
    });

    if (errors.length > 0) {
      errors.forEach((e) => {
        console.error(e.toString());
      });
      process.exit(1);
    }

    this.env = transformed;
  }

  get debug() {
    return this.env.DEBUG;
  }
  
  get postgres() {
    return {
      host: this.env.POSTGRES_HOST,
      username: this.env.POSTGRES_USERNAME,
      password: this.env.POSTGRES_PASSWORD,
    };
  }

  get redis() {
    return {
      host: this.env.REDIS_HOST,
    };
  }
}