public async Task <PrintingEditionsModelItem> GetById(long id) { var response = new PrintingEditionsModelItem(); if (id == 0) { response.Errors.Add(ErrorConstants.ModelIsNull); return(response); } var product = await _printingEditionRepository.GetByProductIdAsync(id); if (product == null) { response.Errors.Add(ErrorConstants.ImpossibleToFindProduct); return(response); } var productModel = PrintingEditionMapper.MapEntityToModel(product.PrintingEdition); foreach (var item in product.Authors) { var author = AuthorMapper.MapEntityToModel(item); productModel.Authors.Add(author); } return(productModel); }