Breaking backward compatibility vs SqlDataReader - rematch

Few weeks ago I wrote about an ugly backward compatibility break in Microsoft SQL Server 2008. So how to write a clean code which works correctly on both 2005 and 2008 and deals with the sp_helpuser issue described in my previous post?

Let's assume that the original code is as follows:

SqlCommand cmd = new SqlCommand();

cmd.Connection = conn;

cmd.CommandType = CommandType.StoredProcedure;

cmd.CommandText = "sp_helpuser";

conn.Open();

SqlDataReader r = cmd.ExecuteReader();

while ( r.Read() )

{

    // throws an exception on SQL Server 2008

    // since GroupName has been renamed to RoleName

    if ( (string)r["GroupName"] ) == "anyvalue" )

       ...

}    

The subtle side issue here is that it's not easy to determine whether a column is or is not available in SqlDataReader. You can try to read a value and catch an exception but this is just slow. However, another, not-so-obvious method has been proposed - please take a look here.

Let's just then add two auxiliary methods:

private bool columnExists( SqlDataReader reader, string columnName )

{

    reader.GetSchemaTable().DefaultView.RowFilter = "ColumnName= '" + columnName + "'";

    return (reader.GetSchemaTable().DefaultView.Count > 0);

}

private string GetGroupRoleName( SqlDataReader reader )

{

    if ( columnExists( reader, "GroupName" ) )

        return (string)reader["GroupName"];

    if ( columnExists( reader, "RoleName" ) )

        return (string)reader["RoleName"];

    /* return something unique */

    return Guid.NewGuid().ToString();

}

and change the original code to:

SqlCommand cmd = new SqlCommand();

cmd.CommandType = CommandType.StoredProcedure;

cmd.CommandText = "sp_helpuser";

conn.Open();

SqlDataReader r = cmd.ExecuteReader();

while ( r.Read() )

{

   // no exception, works on both 2005 and 2008

   if ( GetGroupRoleName( r ) == "anyvalue" )

      ...

}