4

这是我的代码部分：

CResponseVO objCResponseVO = new CResponseVO();

try
{
  var parameters = new DynamicParameters();
  parameters.Add("@UserId", currentUser.userId, DbType.Int32);
  parameters.Add("@Operation", operation, DbType.String);
  parameters.Add("@Output", dbType: DbType.Int32, direction: ParameterDirection.Output);

  using (var connection = SqlAccessHelper.SqlHelper.GetOpenConnection(SqlConnectionHelper.SqlConnectionString()))
  {
    var reader = connection.QueryMultiple("USP_DataExtract", parameters, (SqlTransaction)null, 1000000, CommandType.StoredProcedure);
    int result = parameters.Get<int>("@Output");
    if (operation != "insert")
    {
      ObservableCollection<DataExtraction.DataExtractionTracker> DataExtractionTracker = new ObservableCollection<DataExtraction.DataExtractionTracker>(reader.Read<DataExtraction.DataExtractionTracker>());
      objCResponseVO.addObject("ExtractionStatus", DataExtractionTracker);
    }

  objResponseVO.Result = result;
}

这是我的 SP，我使用try并catch根据输出参数值提交或回滚：

@UserID int=0,
@Operation varchar(50)= NULL,
@Output INT OUTPUT

AS
BEGIN
  BEGIN TRY
    BEGIN TRANSACTION
      If(@Operation = 'select')
      BEGIN
        SELECT RequestId, UserId, RequestTime, Status,DownloadPath from DataExtractTracker where UserId= @UserID
      END

      If(@Operation = 'insert')
      BEGIN
        Insert into DataExtractTracker( UserId, RequestTime, Status) values (@UserID, GETDATE(), 'Waiting')
      END
      SET @Output = 0
    COMMIT TRANSACTION
  END TRY
  BEGIN CATCH
    ROLLBACK TRANSACTION
    SET @Output = 1 
    DECLARE @ErrorMessage NVARCHAR(4000);
    DECLARE @ErrorSeverity INT;
    DECLARE @ErrorState INT;
    SELECT @ErrorMessage = ERROR_MESSAGE(), @ErrorSeverity = ERROR_SEVERITY(),  @ErrorState = ERROR_STATE();

    -- Use RAISERROR inside the CATCH block to return 
    -- error information about the original error that 
    -- caused execution to jump to the CATCH block.
    RAISERROR (@ErrorMessage, -- Message text.
               @ErrorSeverity, -- Severity.
               @ErrorState -- State.);
  END CATCH
END

但是，我无法检索输出参数值。执行时出现异常：

int result = parameters.Get<int>("@Output");

异常是这样说的：

你调用的对象是空的。

4

1 回答 1

9

This is simply a feature of TDS, and you would get the same with ADO.NET; the returned parameter values are usually at the end of the TDS stream; consequently, the updated values are not available until after you have finished consuming the data.

Basically, you need to query the parameter values after you have finished with reader, because until then the value has not come back. For example, the following hastily added integration test passes:

public void TestOutputParameter()
{
    connection.Execute(@"
create proc #TestOutputParameterProc @Foo int, @Bar int out as
set @Bar = @Foo select 1 as [A] select 2 as [B]");
    try
    {
        var args = new DynamicParameters(new { Foo = 123 });
        args.Add("@Bar", dbType: DbType.Int32,
                               direction: ParameterDirection.Output);
        using (var grids = connection.QueryMultiple("#TestOutputParameterProc",
                   args, commandType: CommandType.StoredProcedure))
        {
            // this will fail here; we have not consumed the TDS data yet!
            // args.Get<int>("@Bar").IsEqualTo(123);

            // note we don't *have* to read the data here; disposing "grids"
            // would be enough to skip to the end of the TDS
            grids.Read<int>().Single().IsEqualTo(1); // A
            grids.Read<int>().Single().IsEqualTo(2); // B
        }
        // at this point we have consumed the TDS data, so the parameter
        // values have come back to the caller
        args.Get<int>("@Bar").IsEqualTo(123);
    }
    finally
    { // clean up the proc
        connection.Execute("drop proc #TestOutputParameterProc");
    }
}
于 2013-02-07T08:15:53.513 回答