Question

我有一个查询，它计算一系列日期，我想运行一个不同的查询，只返回年/月组合。我无法弄清楚如何最好地实现这一点。

        private IEnumerable<DateTime> MonthsWithItineraryData (int Id) // shipId
    {
        var months = (from i in context.Itineraries
                          join isd in context.ItineraryStartDates on i.Id equals isd.ItineraryId
                          join id in context.ItineraryDay on i.Id equals id.ItineraryId
                          where i.ShipId == Id
                          select  (DateTime)DbFunctions.AddDays(isd.Date, id.Day)
                          );
        return (months);
    }

Answer 1

我想你想要这样的东西：

return monts.GroupBy(x => new {x.Month, x.Year})
            .Select(x => x.First());

Answer 2

或者你可以将自定义相等比较器作为唯一参数：

public class DateTimeComparer : IEqualityComparer<DateTime> 
{ 
  public bool Equals(DateTime x, DateTime y) 
  { 
    return x.Year == y.Year && x.Month == y.Month; 
  } 
  public int GetHashCode(DateTime obj) 
  { 
    return obj.Year * 100 + obj.Month; 
  } 
} 

result = months.Distinct(new DateTimeComparer()).ToList();

Linq：对计算结果使用Distinct

2 个答案: