A guide on merging decorated parameters to form a unified object in TypeScript

Question

A guide on merging decorated parameters to form a unified object in TypeScript

I'm currently working on a NestJS controller with multiple methods that have a similar structure, like the example below:

@Post(':id/something')
async doSomething(
    @Param('id', ParseUUIDPipe) id: string,
    @Body() body: SomethingDto,
    @AuthUser() updater: IAuthUser,
    @UploadedFiles() attachments: File[],
) {

    // Each method performs a distinct operation and uses a different DTO type,
    // but the parameters remain consistent.
}

In this scenario, Param and Body are from @nestjs/common, AuthUser is a custom decorator, and UploadedFiles is from @nestjs/multer.

I am wondering if there is a way to streamline this by creating a unified parameter decorator that can be implemented for a parameter object.

@Post(':id/something')
async doSomething(@SomeDecorator(SomethingDto) params: Params<SomethingDto>) {
    // Ideal solution would allow me to destructure params like this
    const { id, body, user, attachments } = params;
}

I've come across techniques involving class and property decorators, but nothing applicable to parameter decorators has been found so far.

typescript nestjs decorator

Answer 1

Answer №1

Unfortunately, that option is not currently available.

NestJS operates by injecting values when needed through an internal dependency injection system. In order for this process to work correctly, it must know which values to inject from the start. Without explicitly defining these values, the injection won't occur, as you can't create something out of nothing.

A potential workaround could be to manually inject raw req and res objects using the @Req() and @Res() decorators, but it may be more practical to consider creating a middleware at this stage.

If you're feeling adventurous, delve into the inner workings of NestJS's DI mechanism (which may utilize a third-party package) to understand how it manages value injections for these parameters. This exploration could offer valuable insights.

Answer 2

Unfortunately, that option is not currently available.

NestJS operates by injecting values when needed through an internal dependency injection system. In order for this process to work correctly, it must know which values to inject from the start. Without explicitly defining these values, the injection won't occur, as you can't create something out of nothing.

A potential workaround could be to manually inject raw req and res objects using the @Req() and @Res() decorators, but it may be more practical to consider creating a middleware at this stage.

If you're feeling adventurous, delve into the inner workings of NestJS's DI mechanism (which may utilize a third-party package) to understand how it manages value injections for these parameters. This exploration could offer valuable insights.

Answer 3

Answer №2

Technically speaking, there is a possibility to create a single mega decorator that combines all these functionalities into a custom parameter decorator. However, I strongly advise against this approach. It will result in a complex and hard-to-maintain decorator with minimal validation capabilities. Additionally, it would necessitate the use of intricate DTOs for functionality.

In the event that you still wish to proceed with this method, the implementation will look something like this:

export const SomeMegaDecorator = createParamDecorator((data: unknown, ctx: ExecutionContext) => {
  const req = ctx.switchToHttp().getRequest();
  return {
    params: req.params,
    user: req.user,
    body: req.body,
    files: req.files,
    file: req.file,
    query: req.query
  }
});

You would utilize it as follows:

@SomeMegaDecorator() { params, user, body, files, file, query }: SomeReallyUglyDto

Answer 4

Technically speaking, there is a possibility to create a single mega decorator that combines all these functionalities into a custom parameter decorator. However, I strongly advise against this approach. It will result in a complex and hard-to-maintain decorator with minimal validation capabilities. Additionally, it would necessitate the use of intricate DTOs for functionality.

In the event that you still wish to proceed with this method, the implementation will look something like this:

export const SomeMegaDecorator = createParamDecorator((data: unknown, ctx: ExecutionContext) => {
  const req = ctx.switchToHttp().getRequest();
  return {
    params: req.params,
    user: req.user,
    body: req.body,
    files: req.files,
    file: req.file,
    query: req.query
  }
});

You would utilize it as follows:

@SomeMegaDecorator() { params, user, body, files, file, query }: SomeReallyUglyDto

A guide on merging decorated parameters to form a unified object in TypeScript

Answer №1

Answer №2

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