I've tried to
ObjectScope.GetSqlQuery("TRUNCATE TABLE %table_name%", null, null).Execute();
and
ObjectScope.GetOqlQuery("TRUNCATE TABLE %ClassName%Extent").Execute();
The first row does nothing. And the second throw Exception:
line 1:10: unexpected token: ["TABLE",<42>,line=1,col=10]
Original Query: TRUNCATE TABLE DayExtent