使用 Let 进行子查询的 Linq

我试图从这个 Linq 查询中获取的是所有广告的列表，其中最近关联的日志与LogType.IsStatus == true has a LogType.Name已确认或已更新。需要明确的是，一个 Advert 有很多 Log，每个 Log 有一个 LogType。到目前为止，我有以下内容，但它在 LastOrDefault 上给了我一个错误 System.NotSupportedException。

var adverts = (from a in database.Adverts
                      let lastLog = (from l in a.Logs
                                     where l.LogType.IsStatus == true
                                     orderby l.Created_at
                                     select l).LastOrDefault()
                      where (lastLog != null)
                            &&
                            (lastLog.LogType.Name == "Confirmed" || lastLog.LogType.Name == "Renewed")
                            orderby a.Created_at descending
                      select a).ToList();

LastOrDefault()LINQ to Entities 不支持（请参阅here http://msdn.microsoft.com/en-us/library/bb738550.aspx#sectionSection7).

您可以通过更改来解决此问题order by你的条款let子查询到order by descending然后使用FirstOrDefault()反而。

var adverts = (from a in database.Adverts
               let lastLog = (from l in a.Logs
                              where l.LogType.IsStatus == true
                              orderby l.Created_at descending
                              select l).FirstOrDefault()
               where (lastLog != null)
                     &&
                     (lastLog.LogType.Name == "Confirmed" || lastLog.LogType.Name == "Renewed")
                      orderby a.Created_at descending
               select a).ToList();