Link different datatypes in query builder

Hi,

I am trying to link two tables where one of the links is between two fields with different datatypes, one being a string and the other a numeric. I know how to convert, but I cannot link on converted values. I also tried linking at dataset level and it let me define the link, but no XML result was returned. And when I re opened the data model it removed the link ("DOCO = number (PO)", where DOCO is numeric and PO is a string) saying invalid link removed to null.null. Looks like function lements are not available at the