How to get config in controller route of NestJS?

In NestJS, you can retrieve configuration information within controller routes through multiple methods. Below are some of the most common and effective approaches:

1. Using ConfigService

NestJS includes an official configuration package @nestjs/config, which is based on the dotenv library and allows you to easily access environment variables. First, install the package and import ConfigModule:

bash
npm install @nestjs/config

Then, import ConfigModule into your module:

typescript
import { Module } from '@nestjs/common';
import { ConfigModule } from '@nestjs/config';

@Module({
  imports: [ConfigModule.forRoot()],
})
export class AppModule {}

Within your controller, you can retrieve configuration via dependency injection of ConfigService:

typescript
import { Controller, Get } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';

@Controller('example')
export class ExampleController {
  constructor(private configService: ConfigService) {}

  @Get('config')
  getConfig(): string {
    const someValue = this.configService.get<string>('SOME_CONFIG');
    return someValue;
  }
}

2. Using @Configurable() Decorator

NestJS allows you to dynamically inject configuration values into method parameters. By using the @Configurable() decorator, you can directly inject configuration values into method parameters.

3. Custom Decorator

You can create a custom decorator to inject configuration values, making the code cleaner and more maintainable:

typescript
import { createParamDecorator, ExecutionContext } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';

export const ConfigValue = createParamDecorator(
  (data: string, ctx: ExecutionContext) => {
    const configService = ctx.switchToHttp().getRequest().app.get(ConfigService);
    return configService.get(data);
  },
);

@Controller('example')
export class ExampleController {
  @Get('config')
  getConfig(@ConfigValue('SOME_CONFIG') someValue: string): string {
    return someValue;
  }
}

4. Direct Environment Variable Injection

Another less recommended approach is to directly use process.env within the controller to retrieve environment variables. This method is less flexible and harder to test:

typescript
@Controller('example')
export class ExampleController {
  @Get('config')
  getConfig(): string {
    const someValue = process.env.SOME_CONFIG;
    return someValue;
  }
}

Practical Example:

Suppose you want to retrieve database connection information. You can set the corresponding environment variables in the .env file:

shell
DATABASE_HOST=localhost
DATABASE_PORT=5432
DATABASE_USER=username
DATABASE_PASSWORD=password

Then, within your controller, use ConfigService to retrieve these configuration values:

typescript
@Controller('database')
export class DatabaseController {
  constructor(private configService: ConfigService) {}

  @Get('info')
  getDatabaseInfo(): any {
    const host = this.configService.get<string>('DATABASE_HOST');
    const port = this.configService.get<number>('DATABASE_PORT');
    const user = this.configService.get<string>('DATABASE_USER');
    const password = this.configService.get<string>('DATABASE_PASSWORD');
    
    // In actual applications, for security reasons, you may not directly return password information.
    return { host, port, user };
  }
}

Through this approach, you can securely and efficiently retrieve configuration information within NestJS controller routes, and easily switch between different environments (development, testing, production) using environment variables.