code: public static <D extends Comparable> DateTimeExpression<D> datetrunc(DatePart unit, DateTimeExpression<D> expr) {
          return Expressions.dateTimeOperation(expr.getType(), DATE_TRUNC_OPS.get(unit), expr);
      }
docs: Truncate the given datetime expression
  
  @param unit datepart to truncate to
  @param expr truncated datetime