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[英]Scalar valued function from SQL Server not returning value when called from C#
[英]Returning a scalar from SQL Server to C#
我正在尝试从这样的数据库中返回标量:
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;
这是我的存储过程:
-- =============================================
-- 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
我在ExecuteScalar
行上遇到错误:
System.InvalidOperationException 发生
Message="String[1]: Size 属性的大小为 0 无效。"
我究竟做错了什么?
如果您想使用ExecuteScalar
,您的存储过程需要从SELECT
返回单行单列:
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
然后您的代码需要读取该值:
var returnedValue = cmd.ExecuteScalar();
并从那里使用它。 当然,在这种情况下,您也不需要 C# 代码中的 OUTPUT 参数....
警告词:存储过程中的SELECT
可能会返回多行。 您可能想在 select 中添加TOP 1
- 为了安全起见:
SELECT TOP 1 Field1
FROM dbo.Reasons
WHERE Field1 LIKE @Reason_Number + '%';
只需在存储过程的末尾添加另一条语句并删除OUTPUT
参数
SELECT @Result as 'Result'
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