Date.adddays function not supported in Direct Query Mode ?

Hello 

Trying to add a custom column in Query editor with date function in direct query mode is giving a message "Step is not supported in DIrect Query Mode". 

Function used is -  Date.AddDays([OrderDate],[CustTerms.DueDays])

Order date is already converted to Date format and  Due days is a whole number. Is this not supported in Direct Query mode. What will be the alternative option. I am trying to add number of days to an existing date.