带键和列表的Linq字典

我的数据如下

Master Columns 
ID    MyDateTime 
1     07 Sept
2     08 Sept

上面的MyDatetime列有唯一的索引

Detail Columns
ID     Data1     Data2    Data3
1      a         b        c 
1      x         y        z
1      f         g        h
2      a         b        c

我想在字典中填充它。我试过了

Dictionary<DateTime, List<Detail>> result = (
                          from master in db.master
                          from details in db.detail
                          where (master.ID == detail.ID)
                          select new
                          {
                              master.MyDateTime,
                              details
                          }).Distinct().ToDictionary(key => key.MyDateTime, value => new List<Detail> { value.details });

我期望字典中有两行

1, List of 3 rows as details
2, List of 1 row as details

我得到一个错误，它抱怨字典的键输入两次。关键字是datetime它在主

ILookup<DateTime, Detail> result =
    (from master in db.master
     join details in db.detail on master.ID equals detail.ID
     select new { master.MyDateTime, details })
    .ToLookup(pair => pair.MyDateTime, pair => pair.details);