Function overload

One implementation for many signatures.

Another approach would be to simply receive the categoriesIds in the DTO.

@ArrayNotEmpty()
@ArrayUnique()
@IsCardinal({ each: true })
readonly categoriesIds: number[];

After that, we could transform them to the objects mentioned in the previous solution. For better encapsulation, in the file common -> util -> id.util, create the function wrapId(). We'll use a function overload to have just a single implementation, preventing the need to write two separate functions depending on the parameter (one or many ids). The tooltip adapts depending on the input provided.

export function wrapId(id: number): IdDto;
export function wrapId(ids: number[]): IdDto[];
export function wrapId(idOrIds: number | number[]) {
  if (Array.isArray(idOrIds)) {
    const ids = idOrIds;
    return ids.map((id) => ({ id }));
  }

  const id = idOrIds;
  return { id };
}

Notice the following:

• The last signature is the implementation one, not available when calling

• The return type needs to be explicit when overloading

• The function is used in its regular form (not arrow) to allow for the overload

What remains to be done is to, in the ProductsService, wrap the ids and use them.

create(createProductDto: CreateProductDto) {
  const { categoriesIds } = createProductDto;
  const categories = wrapId(categoriesIds);

  const product = this.productsRepository.create({
    ...createProductDto,
    categories,
  });
  return this.productsRepository.save(product);
}

Commit - Function overload for wrapping ids