Custom Decorators

Nest.js의 Custom Decorators에 대해 정리하였습니다.

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< Param decorators >

You can create your own custom decorators.

 

Ex : @User( ) decorator

In the node.js world, it's common practice to attach properties to the request object. Then you manually extract them in each route handler, using code like the following:

const user = req.user;

 

In order to make your code more readable and transparent, you can create a @User() decorator and reuse it across all of your controllers.

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

export const User = createParamDecorator(
  (data: unknown, ctx: ExecutionContext) => {
    const request = ctx.switchToHttp().getRequest();
    return request.user;
  },
);

@Get()
async findOne(@User() user: UserEntity) {
  console.log(user);
}

 

 

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< Passing data >

you can use the  data  parameter to pass an argument to the decorator's factory function. One use case for this is a custom decorator that extracts properties from the request object by key.

 

Ex)

{
  "id": 101,
  "firstName": "Alan",
  "lastName": "Turing",
  "email": "alan@email.com",
  "roles": ["admin"]
}

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

export const User = createParamDecorator(
  (data: string, ctx: ExecutionContext) => {
    const request = ctx.switchToHttp().getRequest();
    const user = request.user;

    return data ? user?.[data] : user;
  },
);

@Get()
async findOne(@User('firstName') firstName: string) {
  console.log(`Hello ${firstName}`);
}

 

 

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< Working with pipes >

Nest treats custom param decorators in the same fashion as the built-in ones ( @Body() ,  @Param()   and  @Query() ). This means that pipes are executed for the custom annotated parameters as well

 

Ex)

@Get()
async findOne(
  @User(new ValidationPipe({ validateCustomDecorators: true }))
  user: UserEntity,
) {
  console.log(user);
}

: Note that validateCustomDecorators option must be set to true. ValidationPipe does not validate arguments annotated with the custom decorators by default.

 

 

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< Decorator composition >

Nest provides a helper method to compose multiple decorators.

 

Ex)

import { applyDecorators } from '@nestjs/common';

export function Auth(...roles: Role[]) {
  return applyDecorators(
    SetMetadata('roles', roles),
    UseGuards(AuthGuard, RolesGuard),
    ApiBearerAuth(),
    ApiUnauthorizedResponse({ description: 'Unauthorized' }),
  );
}

@Get('users')
@Auth('admin')
findAllUsers() {}

 

 

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Reference : https://docs.nestjs.com/custom-decorators

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