如何从最大长度的嵌套列表中获取列表？

Question

Below is my class structure:

 public class TopLevel
    {
        public int Id { get; set; }
        public List<ChildLevelList> ChildLevelList { get; set; }
    }

public class ChildLevelList
    {
        public int Id { get; set; }
        public List<ChildLevelList1> ChildLevelList1 { get; set; }
    }

public class ChildLevelList1
    {
        public int Id { get; set; }
    }

Now i am trying to get that ChildLevelList1 whose length is highest among all other ChildLevelList1 for each TopLevel records.If found then return that list of ChildListLevel1 for that Top level record

For eg: suppose i have records like below:

TopLevel[0]: ChildLevelList1 (Length =3)
TopLevel[1]: ChildLevelList1 (Length =4)
TopLevel[2]: ChildLevelList1 (Length =8) //get this list
TopLevel[3]: ChildLevelList1 (Length =2)

So I would like to get ChildLevelList for TopLevel 2 ie from third position like below:

Output:[2]: ChildLevelList1 (Length =8)

I am trying to get in below variable:

var childLevelList1 // trying to get in this varaible

This is how I am trying:

for (int i = 0; i < List.Count(); i++)
        {
           //Sorry  but not getting how to do this.    
        }

Answer 1

First of all I choose some better names to avoid confusion

public class TopLevel
{
    public int Id { get; set; }
    public List<ChildLevel> ChildLevelList { get; set; }
}

public class ChildLevel // was ChildLevelList
{
    public int Id { get; set; }
    public List<ChildLevel1> ChildLevelList1 { get; set; }
}

public class ChildLevel1 // was ChildLevel1List
{
    public int Id { get; set; }
}

And to get the List with the highest length

public List<ChildLevel1> GetBiggestChildLevel1List( IEnumerable<TopLevel> source )
{
    return source
        .SelectMany( t => t.ChildLevelList )   // IEnumerable<ChildLevel>
        .Select( c1 => c1.ChildLevelList1 )    // IEnumerable<List<ChildLevel1>>
        .OrderByDescending( c2l => c2l.Count ) // IEnumerable<List<ChildLevel1>>
        .FirstOrDefault();
}

Answer 2

您将从TopLevel下降了两个级别，因此可以尝试使用以下LINQ查询：

var result = List.OrderByDescending(x => x.ChildLevelList.Select(y => y.ChildLevelList1.Count())).First();