Question

I am trying to return scalar from a database like this:

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;

Here is my stored procedure:

-- =============================================
-- 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

I am getting an error on the ExecuteScalar line:

System.InvalidOperationException occurred
Message=”String[1]: the Size property has an invalid size of 0.”

What am I doing wrong?

Answer 1

If you want to use ExecuteScalar, your stored proc needs to return the single row, single column from a SELECT:

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

and then your code needs to read that value:

var returnedValue = cmd.ExecuteScalar();

and use it from there. Of course, in that case, you also do not need an OUTPUT parameter in your C# code….

Word of warning: that SELECT in your stored proc could potentially return multiple rows. You might want to add a TOP 1 to your select – just to be safe:

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