public ActionResult Index(MillingCutter Cutter)
        {
            decimal? D = Cutter.D;
            decimal? d1 = Cutter.d1;
            decimal? ap = Cutter.ap;
            decimal? L = Cutter.L;
            IQueryable<MillingCutter> cutters = db.MillingCutters;
            if (D != null) cutters = cutters.Where(c => c.D == D);
            if (d1 != null) cutters = cutters.Where(c => c.d1 == d1);
            if (ap != null) cutters = cutters.Where(c => c.ap == ap);
            if (L != null) cutters = cutters.Where(c => c.L == L);
            return View(cutters);
        }

public static IQueryable<T> Where<T>(this IQueryable<T> src, Expression<Func<T, bool>> exp, Func<T> value)
        {
            if (value() == null)
                return src;
            return src.Where(exp);
        }