OleDbCommand not returning results vs SqlCommand

Question

I'm trying to change my program from an SqlConnection to an OleDbConnection but I've hit a little block.

My program works as expected using SqlConnection but I can't get it to work with OleDb .

My program reads the results of a stored procedure (XML), sends it to a web service, then stores the results in a table.

I'm having issues with reading the XML from the stored procedure.

Here's my code for the first part:

public static bool BuildXml()
{
    using (OleDbCommand buildXml = new OleDbCommand("usp_BUILD_RISKCALC_XML", SqlOleDbConnection))
    {
       buildXml.CommandType = CommandType.StoredProcedure;

       try
       {
           OleDbDataReader reader = buildXml.ExecuteScalar();

           while (reader.Read())
           {
               SendXml = reader.GetString(0);
           }
        }
        catch (Exception ex)
        {
             WriteLog(ex.Message, 101);
                return false;
        }
    }
} 

I'm getting an InvalidOperationException the text of which reads

Specified cast is not valid

For reader.GetString(0) .

I am 100% sure the stored procedure is working as I have tested using an SqlConnection as well as running in SQL Server Management Studio.

Answer 1

Your code should be;

public static bool BuildXml()
{
     using (OleDbCommand buildXml = new OleDbCommand("usp_BUILD_RISKCALC_XML", SqlOleDbConnection))
     {
          buildXml.CommandType = CommandType.StoredProcedure;

          try
          {
               object value = buildXml.ExecuteScalar();
               SendXml = Convert.ToString(value);
          }
          catch (Exception ex)
          {
               WriteLog(ex.Message, 101);
               return false;
          }
     }
}

The code buildXml.ExecuteScalar() returns an object. So casting it to an OleDbDataReader will end up in the InvalidOperationException .

Answer 2

ExecuteScalar return type's is object and you can't convert it to OleDbDataReader . When you have used ExecuteScalar means that you are sure that you want to return only one value from your stored procedure. You don't need OleDbDataReader just try following:

SendXml = buildXml.ExecuteScalar().ToString;