LINQ 查询 NotSupportedException OrderBy 平均时间跨度

Question

var seasonPlayer = (from SeasonPlayer in db.SeasonPlayerSet 
                    orderby SeasonPlayer.StatisticsPlayer.Average(x => x.STP_timeplay.Ticks) descending 
                    select SeasonPlayer).ToList();

SeasonPlayer 有一个 StatisticsPlayer 的 ICollection，所以我想获得在球场上花费的平均时间，按 STP_timeplay 降序排列，这是 TimeSpan 的一个典型值。我无法通过 STP_timeplay 获取平均值，因为它不是小数，所以我尝试通过 Ticks 获取平均值。它抛出一个异常：

The specified type member 'Ticks' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.

Answer 1

问题是 Linq to Entities 查询提供程序无法将您的 LINQ 转换为 Sql 查询，该查询连接到 Statistics Player，平均时间播放，按季节播放器分组。

鉴于您似乎在迭代所有赛季球员，如果记录的数量不是太大，您可以像这样将这些全部记入内存：

var seasonPlayer = db.SeasonPlayerSet
                      .Include(sp => sp.StatisticsPlayer)
                      .ToList()
                      .Select(sp => new {SeasonPlayer = sp, Average = sp.StatisticsPlayer.Average(stp => stp.STP_timeplay.Ticks)})
                      .OrderByDescending(sp => sp.Average)
                      .Select(sp => SeasonPlayer)
                      .ToList();

Answer 2

试试这个：-

var seasonPlayer = db.SeasonPlayerSet.ToList()
                     .OrderByDescending(x => x.StatisticsPlayer
                                             .Average(z => z.STP_timeplay.Ticks);