[英]Creating a tree with LINQ expression
我有一個由存儲過程返回的以下字段的C#列表:
CarrierId ParentCarrierId Name Descrition
1 NULL A AA
2 1 B BB
3 1 C CC
4 3 D DD
5 NULL E EE
我需要從這個輸出中構造一個嵌套對象列表
所以Carrier的每個對象都應該包含所有孩子的列表。 任何人都可以幫我構建一個LINQ代碼來實現這一目標嗎?
期望的結果:
CarrierId = 1
|__________________ CarrierId = 2
|__________________ CarrierId = 3
|___________________ CarrierId = 4
CarrierId = 5
期望的結果應如上所述
首先創建一個將父ID映射到其子項的查找:
var lookup = carriers.ToLookup(carrier => carrier.ParentCarrierId);
遍歷每個節點並根據查找分配其子節點:
foreach(var carrier in carriers)
carrier.Children = lookup[carrier.CarrierId];
要獲取所有根節點,只需從查找中獲取空值:
var roots = lookup[null];
注意,整個操作是O(n),因為構建查找是O(n),並且每個單載波的所有子節點都可以在O(n)時間內找到,而不是將O(n ^ 2)時間視為在發布的其他解決方案中(因為他們使用O(n)操作來查找單個節點的所有子節點)。 這使得此代碼比其他選項快得多,而且更簡單,更短。
你原來的問題有點不同。 我認為每個運營商都應該列出所有后代的清單。 現在看來你只想抱着所有直接的孩子。 這很簡單:
c.Children = carrierList.Where(child => child.ParentCarrierId == c.CarrierId).ToList();
如果你想要它作為LINQ查詢,那么你必須創建Carrier
新實例:
List<Carrier> rootCarriers = carrierList
.Select(c => new Carrier {
CarrierId = c.CarrierId,
Name = c.Name,
Descrition = c.Descrition,
ParentCarrierId = c.ParentCarrierId,
Children = carrierList
.Where(child => child.ParentCarrierId == c.CarrierId)
.ToList()
})
.Where(c => !c.ParentCarrierId.HasValue)
.ToList();
該查詢還根據需要刪除所有不是根載波(具有父節點)。
以下顯示了兩種不同屬性Children
和Descendants
,后者甚至返回孫子等等。
public class Carrier
{
public List<Carrier> Descendants { get; set; }
public List<Carrier> Children { get; set; }
public static IEnumerable<Carrier> TraverseDescendants(IEnumerable<Carrier> allCarriers, Carrier rootCarrier)
{
Queue<Carrier> queue = new Queue<Carrier>();
var children = allCarriers.Where(c => c.ParentCarrierId == rootCarrier.CarrierId);
foreach (Carrier c in children)
queue.Enqueue(c);
while (queue.Count > 0)
{
Carrier child = queue.Dequeue();
yield return child;
var grandchildren = allCarriers.Where(c => c.ParentCarrierId == child.CarrierId);
foreach (Carrier c in grandchildren)
queue.Enqueue(c);
}
}
}
使用TraverseDescendents
您可以初始化班級中的List<Carrier> Descendents
。 Children
-list是一個簡單的LINQ查詢:
foreach (Carrier c in carrierList)
{
c.Descendants = Carrier.TraverseDescendants(carrierList, c).ToList();
c.Children = carrierList.Where(child => child.ParentCarrierId == c.CarrierId).ToList();
}
如果你添加一個public List<Carrier> Children { get; set; }
這將對內存中的可承運的運營商起作用public List<Carrier> Children { get; set; }
public List<Carrier> Children { get; set; }
public List<Carrier> Children { get; set; }
屬性到你的Carrier級。
public static class CarrierExt
{
public static List<Carrier> AsTree(this IEnumerable<Carrier> carriers)
{
return carriers.AsTree(null);
}
private static List<Carrier> AsTree(this IEnumerable<Carrier> carriers, int? parentId)
{
return (from carrier in carriers
where carrier.ParentCarrierId == parentId
let children = carrier.Children = carriers.AsTree(carrier.CarrierId)
select carrier).ToList();
}
}
編輯:請注意,這會將頂級列表減少到只有2個根元素。
試試這個
class Program
{
static void Main(string[] args)
{
IList<Carrier> CarrierList = new List<Carrier>();
CarrierList.Add(new Carrier { CarrierId = 1, Name = "A", Description = "AA", ParentCarrierId = null });
CarrierList.Add(new Carrier { CarrierId = 2, Name = "B", Description = "BB", ParentCarrierId = 1 });
CarrierList.Add(new Carrier { CarrierId = 3, Name = "C", Description = "CC", ParentCarrierId = 1 });
CarrierList.Add(new Carrier { CarrierId = 4, Name = "D", Description = "DD", ParentCarrierId = 3 });
CarrierList.Add(new Carrier { CarrierId = 5, Name = "E", Description = "EE", ParentCarrierId = null });
Temp temp = new Temp();
IList<Carrier> CarrierList1=new List<Carrier>();
foreach (Carrier carrier in CarrierList.Where(p => p.ParentCarrierId == null).ToList() )
{
CarrierList1.Add(temp.Recursive(carrier, CarrierList));
}
}
}
public class Temp
{
public Carrier Recursive(Carrier carrier,IList<Carrier> carrierList)
{
if (carrierList.Where(c => c.ParentCarrierId == carrier.CarrierId).Count() <1)
{
return carrier ;
}
else
{
IList<Carrier> newList = new List<Carrier>();
foreach (Carrier ca in carrierList.Where(c => c.ParentCarrierId == carrier.CarrierId)){
newList.Add(Recursive(ca, carrierList));
}
carrier.CarrierList = newList;
return carrier;
}
}
}
public class Carrier
{
public int CarrierId { get; set; }
public string Name { get; set; }
public string Description { get; set; }
public int? ParentCarrierId { get; set; }
public IList<Carrier> CarrierList { get; set; }
}
}
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