public IActionResult AddBookToLibrary(long idLibrary, [FromBody] MyLibrary item) { if (item == null || item.libraryid != idLibrary) { return(BadRequest()); } var library = libraryRepository.FindByID(idLibrary); if (library == null) { return(NotFound("Could not find library with id : " + idLibrary + ". Please try again with valid id.")); } library.myBooks = item.myBooks; MyLibrary updatedLibrary = libraryRepository.AddBookToLibrary(library); if (updatedLibrary.libraryid == -1) { return(NotFound("Invalid book id : " + updatedLibrary.libraryname + ". Please try again")); } if (updatedLibrary.libraryid == -2) { return(NotFound("Book id : " + updatedLibrary.libraryname + " already present in same library. Please try again by removing that id")); } if (updatedLibrary.libraryid == -3) { return(NotFound("Book id : " + updatedLibrary.libraryname + " is present in another library. \nPlease use ChangeLibrary endpoint if you want to move book to another library")); } return(CreatedAtRoute("AddBookToLibrary", new { idLibrary = idLibrary }, updatedLibrary)); }