Field names access by string

I use the following code to refer to a field from the database:

Predicate<object> predicate1 = (Q => ((tblResource)Q).FldShortName == "john")

where tblResource is the name of the table and FldShortName is the name of the field.

All works well but how do you use the above if the field name is not hard coded but is instead a string value?