public IHttpActionResult AddProduct(int id, [FromBody] AddProductToAuthorRequest request)
 {
     try
     {
         Author author = authorRepository.getById(id);
         if (productRepository.exists(request.ProductId))
         {
             author.Products.Add(productRepository.getById(request.ProductId));
             db.SaveChanges();
             return(Ok(author));
         }
         else
         {
             return(BadRequest("Product does not exist"));
         }
     }
     catch (Exception e)
     {
         return(NotFound());
     }
 }