返回從SQL Server到C＃

Question

我想從這樣的數據庫返回標標：

DbConnection cn = GetConnection2(); 
cn.Open(); 

// stored procedure 
DbCommand cmd = GetStoredProcCommand(cn, "GetReason"); 
DbParameter param; 

param = CreateInParameter("Reason_Number", DbType.String); 
param.Value = number; 
cmd.Parameters.Add(param); 

param = CreateOutParameter("Result", DbType.String); 
param.Direction = ParameterDirection.Output; 
cmd.Parameters.Add(param); 

cmd.ExecuteScalar(); 

string reason; 
reason = cmd.Parameters["@Result"].Value.ToString(); 

if (cn.State == ConnectionState.Open) 
    cn.Close(); 

return reason; 

這裏是我的存儲過程：

-- ============================================= 
-- Create date: Today 
-- Description: Input Reason # and Return Full Reason Name 
-- ============================================= 
ALTER PROCEDURE [dbo].[GetReason] 
    @Reason_Number nvarchar(50), 
    @Result nvarchar(50) output 
AS 
BEGIN 
    -- SET NOCOUNT ON added to prevent extra result sets from 
    -- interfering with SELECT statements. 
    SET NOCOUNT ON; 

    SELECT @Result = Field1 
    FROM dbo.Reasons 
    WHERE Field1 LIKE @Reason_Number + '%'; 
END 

我就收到一個錯誤ExecuteScalar行：

System.InvalidOperationException發生
消息=「字符串[1]：第e Size屬性的無效大小爲0.「

我在做什麼錯？

Answer 1

如果你想使用ExecuteScalar，你的存儲過程需要從SELECT返回單行，單柱：

ALTER PROCEDURE [dbo].[GetReason] 
    @Reason_Number nvarchar(50) 
AS 
BEGIN 
    -- SET NOCOUNT ON added to prevent extra result sets from 
    -- interfering with SELECT statements. 
    SET NOCOUNT ON; 

    SELECT Field1 
    FROM dbo.Reasons 
    WHERE Field1 LIKE @Reason_Number + '%'; 
END 

，然後你的代碼需要讀取值：

var returnedValue = cmd.ExecuteScalar(); 

並從那裏使用它。當然，在這種情況下，你也不必OUTPUT參數在C＃代碼....

字的警告：即SELECT在你的存儲過程可能可能返回多行。你可能想一個TOP 1添加到您的選擇 - 只要是安全的：

SELECT TOP 1 Field1 
    FROM dbo.Reasons 
    WHERE Field1 LIKE @Reason_Number + '%'; 

Answer 2

只需添加另一個語句將存儲過程的結束和刪除OUTPUT參數

SELECT @Result as 'Result'