Linq带有子查询

Question

我想从这个Linq查询得到的是所有广告的列表,其中最近关联的日志与a LogType.IsStatus == true具有LogType.Name已确认或已更新.要清楚,广告有许多日志,每个日志有一个LogType.到目前为止,我有以下内容,但它在LastOrDefault上给出了一个错误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();

Answer 1

LastOrDefault()LINQ to Entities不支持(请参阅此处).

您可以通过将子查询中的order by子句更改let为a order by descending然后再使用FirstOrDefault()来解决此问题.

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();