Question

所以，我有一段代码

var _activeContract = (from cnt in UnitOfWork.Context.Contract.Where(w => w.IS_DELETED == 0 && w.CONTRACT_STATUS_ID == (int)NemsKysContractStatusEnum.Aktif)
    join sei in UnitOfWork.Context.SiteExtendedInfoList.Where(w => w.IS_DELETED == 0) on cnt.SITE_ID equals sei.SITE_ID
    join sr in UnitOfWork.Context.Subregion.Where(w => w.IS_DELETED == 0) on sei.RN_SUBREGION_ID equals sr.ID
    join r in UnitOfWork.Context.Region.Where(w => w.IS_DELETED == 0) on sr.REGION_ID equals r.ID
    join mr in UnitOfWork.Context.MainRegion.Where(w => w.IS_DELETED == 0) on r.MAIN_REGION_ID equals mr.ID
    select new { MRNAME = mr.NAME, cnt.ID }).GroupBy(g => g.MRNAME).OrderBy(t => t.Key).Select(s => new { name = s.Key, data = s.Count() }).ToList();

我无法理解最后一行。

据我所知，创建输出序列时，它的每个元素都是
{ MRNAME = mr.NAME, cnt.ID }即非对象。然后我们按MRNAME对此序列进行分组，然后按Key（部分OrderBy(t=>t.Key)）对其进行排序。 Key是什么？这把钥匙来自哪里？因为我们只有两个字段：MRNAME和cntID，不是吗？

然后我无法理解如何 Select(s => new { name = s.Key, data = s.Count() })有效。它在前一个{ MRNAME = mr.NAME, cnt.ID }个对象序列的每个元素上创建一个新序列，其中每个元素都是{ name = s.Key, data = s.Count() }之类的对象。

我再次理解Key在这里是什么以及我们计算的是s.Count()计算字段数据，我们究竟计算了什么？

Answer 1

  from ...
  select new { MRNAME = mr.NAME, cnt.ID })  //1
.GroupBy(g => g.MRNAME)  //2
.OrderBy(t => t.Key)  //3
.Select(s => new { name = s.Key, data = s.Count() })  //4
.ToList();

GroupBy输出的每个元素都是一个IGrouping，它具有Key属性。

通过调用读取代码调用：

//1 Each element has MRName and ID properties.
//2 Group the elements by the MRName property, we now have a query consisting of groups.
//3 Order the groups by the Key, which is the MRName property.
//4 Turn each group into a new element.  Each element has a name and data property.

这个查询如何工作？

1 个答案: