XDataProperty and Xdata build in functions


In underlying table I have timestamp with separate columns (creationdate and creationtime) but in xdata I would love to send / receive them as one field "created".
It works nicely with XDataProperty and XDataExcludeProperty attributes. 
But then i wan't to search for example ?filter=day('created') eq 30, I'll get error.
There isn't probably any way to fix this?

All Aurelius and XData queries are performed directly in the database. The $filter string is converted directly into an SQL statement, there are no in-memory filters. Thus, you can only use there properties that are directly mapped in the database.