存储过程在管理工作室中返回值,但不在c#代码中

Question

我有一个存储过程使用链接服务器(ADSI)连接到活动目录.它接受一个字符串/ varchar guid,然后将用户的thumbnailPhoto属性从活动目录中返回.我试图从C#代码调用此过程,但它一直返回null.我试图确保传递的guid是正确的,所以从调试,我抓住guid被传递到参数然后尝试使用它来管理工作室中的sproc.结果很好,但是当我从我的应用程序中执行它时,我得到null.这是代码:

存储过程:

ALTER PROC [dbo].[sp_GetPhotoFromADSI] 
                @GUID varchar(100)
AS 
                SET NOCOUNT ON 
                SET XACT_ABORT ON  

                BEGIN TRAN

                DECLARE @sql NVARCHAR(600)

                SET @sql=N'SELECT thumbnailPhoto FROM OPENQUERY(ADSI,
                                ''SELECT thumbnailPhoto 
                                  FROM ''''LDAP://<GUID=' + @GUID + '>'''' 
                                  WHERE objectCategory = ''''Person'''' AND objectClass = ''''user'''''')'

                EXEC SP_EXECUTESQL @sql

                COMMIT

C#:

private byte[] GetUserPhotoByGuid(Guid userNativeGuid)
{
    //dont judge me for not abstracting this
    var connString = "connectionStringCrap;";
    byte[] photo = null;

    using (var conn = new SqlConnection(connString))
    {
        try
        {
            string guidString = userNativeGuid.ToString();

            //var realGuid = Guid.Parse(userNativeGuid);
            using (var comm = new SqlCommand("sp_GetPhotoFromADSI", conn))
            {
                comm.CommandType = CommandType.StoredProcedure;
                comm.Parameters.AddWithValue("@GUID", guidString);
                var returnParameter = comm.Parameters.Add("@Output", SqlDbType.Binary);
                returnParameter.Direction = ParameterDirection.ReturnValue;
                conn.Open();
                comm.ExecuteScalar();

                photo = returnParameter.Value as byte[];
                return photo;                       
            }
        }
        catch (Exception)
        {
            throw;
        }
        finally
        {
            conn.Close();
        }

    }
    return null;
}

Answer 1

该值将返回ExecuteScalar().

Byte[] photo = (Byte[])comm.ExecuteScalar();