def code_system_pairs
      codes.collect do |code|
        { code: code.code, system: code.codeSystem }
      end
    end
def code_system_pairs
      codes.collect do |code|
        { code: code.code, system: code.codeSystem }
      end
    end
Returns all of the codes on this datatype in a way that is typical
 to the CQL execution engine.