c# - 从平面表中表示的父/子关系创建树

Question

我有一个由存储过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

我需要根据这个输出构造一个嵌套的对象列表

所以 Carrier 的每个对象都应该有它所有子对象的列表。任何人都可以帮助我构建 LINQ 代码来完成此任务吗？

期望的结果:

  CarrierId = 1
      |__________________ CarrierId = 2
      |
      |__________________ CarrierId = 3
      |
      |                        |___________________ CarrierId = 4
CarrierId = 5

期望的结果应该如上所述

下面的代码在树中排列事物，但一个 child 仍然出现在列表中

c.Children = carrierList.Where(child => child.ParentCarrierId == c.CarrierId).ToList();



 CarrierId = 1
      |
      |__________________ CarrierId = 2
      |
      |__________________ CarrierId = 3
      |                        |___________________ CarrierId = 4
      |

 CarrierId = 2

      |
 CarrierId = 3

      |
 CarrierId = 4

      |
 CarrierId = 5

我不想要这种行为。如果某物显示为 Child，则应将其从 root 中删除。

Answer 1

这就是您所需要的。

首先，从源数据开始:

var source = new []
{
    new { CarrierId = 1, ParentCarrierId = (int?)null, Name = "A", Description = "AA", },
    new { CarrierId = 2, ParentCarrierId = (int?)1, Name = "B", Description = "BB", },
    new { CarrierId = 3, ParentCarrierId = (int?)1, Name = "C", Description = "CC", },
    new { CarrierId = 4, ParentCarrierId = (int?)3, Name = "D", Description = "DD", },
    new { CarrierId = 5, ParentCarrierId = (int?)null, Name = "E", Description = "EE", },
};

然后，通过 ParentCarrierId 创建一个查找:

var lookup = source.ToLookup(x => x.ParentCarrierId);

现在我们需要一个输出结构:

public class Carrier
{
    public int Id;
    public List<Carrier> Children = new List<Carrier>();
    public string Name;
    public string Description;
}

然后，一个 build 函数通过 ParentCarrierId 弹出所有的载体:

Func<int?, List<Carrier>> build = null;
build = pid =>
    lookup[pid]
        .Select(x => new Carrier()
        {
            Id = x.CarrierId,
            Name = x.Name,
            Description = x.Description,
            Children = build(x.CarrierId),
        })
        .ToList();

注意:它是递归的，因此需要使用初始 = null 来定义它。

最后我们构建:

List<Carrier> trees = build(null);

这给出: