group by multiple columns in linq to sql c#

This is basically used for "How to Group By multiple columns in LINQ to SQL?"

[Route("API/Use/GetUsageAlerts/{UserID}/{AccountID}")]

public IEnumerable<UsageAlerts> GetUsageAlerts(int UserID, int AccountID)

{

      DALUse ObjDalUse = new DALUse();

      Mapper mapper = new Mapper();

      List<UsageAlerts> usedAlerts = mapper.MapDALUsageAlerts2BAL(ObjDalUse.getAllUsageAlerts(UserID, AccountID));

     List<UsageAlerts> userUsages = (from used in usedAlerts

                              group used by used.ProductServiceId into res

                              select new UsageAlerts

                              {

                                 UsageIncluded = res.Sum(l => l.UsageIncluded),

                                 UsedUnit = Convert.ToString(res.Sum(m => int.Parse(m.UsedUnit))),

                                 Product = Convert.ToString(res.Max(l => l.Product)),

                                 ProductServiceId = res.Key

                               }).ToList();

    return userUsages;

 }