asp.net中创建的GUID无法存储到数据库中的事情.请帮忙,该如何处理

asp.net中创建的GUID无法存储到数据库中的事情...请帮忙
这是生成GUID的代码.我测试了是正确的可以生成..  
private static string shoppingCartId
  {
  get
  {
  HttpContext current = HttpContext.Current;
  string str = "";
  object obj2 = current.Session["bookShop_CartID"];
  if (obj2 != null)
  {
  str = obj2.ToString();
  }
  if (str != null)
  {
  return str;
  }
  if (current.Request.Cookies["bookShop_CartID"] != null)
  {
  str = current.Request.Cookies["bookShop_CartID"].Value;
  current.Session["bookShop_CartID"] = str;
  return str;
  }
  else
  {
  str = Guid.NewGuid().ToString();
  HttpCookie cookie = new HttpCookie("bookShop_CartID", str.ToString());
  int cartPersistDays = configuration.CartPersistDays;
  DateTime now = DateTime.Now;
  TimeSpan span = new TimeSpan(cartPersistDays, 0, 0, 0);
  DateTime time2 = now.Add(span);
  cookie.Expires = time2;
  current.Response.Cookies.Add(cookie);
  current.Session["bookShop_CartID"] = str;
  return str.ToString();
  }
  }
  }


我是这样调用的
  SqlCommand command = DataAccess.CreateCommand();
  command.CommandText = "ShoppingCartAddItem";
  SqlParameter parameter = command.CreateParameter();
  parameter.ParameterName = "@cartID";
  parameter.Value = shoppingCartId;
  parameter.SqlDbType = SqlDbType.Char;
  parameter.Size = 0x24;
  command.Parameters.Add(parameter);
  parameter = command.CreateParameter();
  parameter.ParameterName = "@bookID";
  parameter.Value = bookID;
  parameter.SqlDbType = SqlDbType.Int;
  command.Parameters.Add(parameter);
为什么GUID没有存到数据库里呢...数据库里的那个字段是空的什么也没有,请帮忙

------解决方案--------------------------------------------------------
parameter.SqlDbType = SqlDbType.UniqueIdentifier; 

------解决方案--------------------------------------------------------

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parameter.SqlDbType = SqlDbType.UniqueIdentifier;