public IQueryable <ThietBi> GetBooks([QueryString("id")] int?categoryId)
        {
            var _db = new ThietBiOnLine.Models.ThietBiContext();
            IQueryable <ThietBi> query = _db.ThietBis;

            if (categoryId.HasValue && categoryId > 0)
            {
                query = query.Where(p => p.HangID == categoryId);
            }
            return(query);
        }
        public IQueryable <ThietBi> GetDetails([QueryString("bookID")] int?bookId)
        {
            var _db = new ThietBiOnLine.Models.ThietBiContext();
            IQueryable <ThietBi> query = _db.ThietBis;

            if (bookId.HasValue && bookId > 0)
            {
                query = query.Where(p => p.ThietBiID == bookId);
            }
            else
            {
                query = null;
            }
            return(query);
        }