Linq分组与孩子的情况

Question

我有ORM数据类型，如下所示

public class PackData
{
   public int PackId
   public int ClientId
   public DateTime DateCreated
   public List<PackItemData> PackItems
}

public class PackItemData
{
   public int PackId
   public string DeviceId
}

我可以使用Linq查询PackData和PackItemData

var data = DataTable.Where(pack =>  pack.DateCreated >= startDate 
                                    && pack.DateCreated <= endDate)

我想分组/区分子数据（PackItemData）以获取设备ID的唯一结果

我怎样才能做到这一点？

Answer 1

我认为您正在寻找SelectMany。这会使您的List<List<PackItemData>>变为List<PackItemData>

var data=DataTable.Where(pack =>  pack.DateCreated >= startDate 
                                  && pack.DateCreated <= endDate)
                   .SelectMany(i => i.PackItems)
                   .GroupBy(i => i.DeviceId).Select(i => i.First());

Answer 2

var groups = DataTable
    .Where(pack => pack.DateCreated >= startDate && pack.DateCreated <= endDate)
    .SelectMany(pack => pack.PackItems)
    .GroupBy(item => item.DeviceId);

您可能希望从SelectMany开始，这将允许您枚举所有PackDatas中的所有PackItem。这会为您提供IEnumerable<PackItemData>，然后您可以在分组中使用它。

Answer 3

Linq GroupBy和不同的方法可以满足您的需求。

var data=DataTable.Where(pack => pack.DateCreated >= startDate && pack.DateCreated <= endDate)
                  .Select( pack => pack.PackItems)
                  .GroupBy( p => p.PackId, p => p.DeviceId, (key, p) => new PackItemData { PackId = key, DeviceId = p});

我不是100％这是有效的，因为我还没有进行测试，但这应该让你接近你要去的地方。

来源：Group by in LINQ

Answer 4

 var data = DataTable.Where(pack =>  pack.DateCreated >= startDate 
                              && pack.DateCreated <= endDate).SelectMany(s=> s.PackItems).GroupBy(p => p.DeviceId).Select(r=> r);

我认为这应该有用。