using(TransactionScope scope = new TransactionScope(TransactionScopeOption.Required, new TransactionOptions {IsolationLevel = IsolationLevel.RepeatableRead}))
{
     PersonDayStatisticsUnit pdsu = db.PersonDayStatisticsUnits.FirstOrDefault(x => x.UnitId == su.Id && x.Date == now && x.PersonAnonimousGuid == personGuid);
     if (pdsu == null)
     {
         pdsu = new PersonDayStatisticsUnit()
         {
             UnitId = su.Id,
                 Count = 1,
                 Date = now,
                 PersonAnonimousGuid = personGuid
         };
         db.PersonDayStatisticsUnits.Add(pdsu);
         ret = true;
     }
     else
     {
         pdsu.Count++;
         ret = false;
     }

     db.SaveChanges();

     scope.Complete();
 }