I am working on a WebAPI application which follows the layered approach like Controller > Service Layer > Repository Layer > Entity Framework Core (SQL / Cosmos) The view is in Angular.

In many of our API, we have some transformation required on the Request object (DTO - request send by UX) to a domain entity that my repository understands. This transformation usually is handled in the Service layer. This is the standard approach I think.

Now I have an Request object (DTO - request sent by UX, shown below) which is a simple class and I don't need any transformation from DTO to Domain entity. Infact I have a DbSet matching exactly this and the database table has exactly these 3 columns only. In this case, I end up doing the transformation from DTO to Domain entity unnecessarily.

    public class BookDTO //Received in the API request
    {
        public string Name { get; set; }
        public string Author { get; set; }
        public decimal price { get; set; }
    }

To avoid this pointless mapping / transformation I can use the same DTO across all the layers (Controller to Service to Repository), But I feel this is not the right way to do. (Do let me know if there is nothing wrong with this approach)

Essentially either I will be doing a transformation of DTO to domain model when they have absolutely same attributes or I will end up referencing the DTO in all layers including the repository as well.

I am not sure if these are the only two options for me or there is a gap in my understanding.