linq-to-sql - 如何通过 LINQ to Sql 结果上的数据对分组进行 lambda？

Question

1. 我像这样从数据库中获取数据。

    Dim query = From t1 In TBL1 _
                Join t2 In TBL2 On t1.ID Equals t2.ID _
                Join t3 In TBL3 On t1.ID Equals t3.ID _
                Group Join t4 In t1 _
                      On t1.ID Equals t4.ID _
                      Into t4_Grp = Group _
                Select t1, t2, t3, t4_Grp
   

2. 当用户执行搜索时，我可以像这样过滤查询结果。

   query = query.Where(Function(o) o.t1.ID = lngID)
   

3. 上面一切正常。直到我想 lambda t4_Grp。我不知道如何在 t4_Grp 上做一个 lambda 表达式？

Answer 1

我过去用它来做一些权力分组。

private void ProducePivotAnalytic <T, K>(IEnumerable<T> colletion, Func<T, K> pivot)
{
    var grouped =
        from n in colletion
            group n by pivot(n) into g
            select new { theKey = g.Key, theValue = g };
    // do some stuff with your grouped collection.
}


ProducePivotAnalytic<List<DateTime>, DayOfWeek>(
        myDates,
            (x) => (x.DayOfWeek) );