Question

鉴于以下类...

public class Category {
  public string Name {get;set;}
  public Category ParentCategory {get;set;}
}

从类别对象的集合（IList<Category>）中输出以下内容的最有效方法是什么？

+ Parent Category
++ Sub Category
++ Sub Category 2
+ Parent Category 2
++ Sub ...
++ Sub ..
++ Sub ....

编辑：也许真正的问题应该是，我应该如何在数据库中表示这个模型，并使用 NHibernate 检索它？

Answer 1

您可以考虑反转您的关系。如果一个节点可以到达其父节点但反之则不行，则必须拥有所有叶节点才能打印出完整的树形结构。将其与每个节点都知道其子节点的情况进行比较-那么您只需要根节点即可。

Answer 2

一个小的递归函数就能为您完成它。

static void recurseCategories(ref List<Category> cl, Category start, int level)
{
  foreach (Category child in cl)
  {
    if (child.ParentCategory == start)
    {
      Console.WriteLine(new String(   , level) + child.Name);
      recurseCategories(ref cl, child, level + 1);
    }
  }
}

我的假设是：

You ve got an List of Category. (Of course all Category objects you want to print must be in that list. I thought that was self-evident, but seemingly it was not.)
The root category has a parent of null. The initial function call should therefore be recurseCategories(ref myCategoryList, null, 0).
No orphaned elements exist in your list. Some error handling code should be added.
Output order will be coherent to whatever order the list is iterated, so apart from the hierarchy it s more or less coincidental.

Answer 3

最近我了解了层次化Linq查询，查看http://weblogs.asp.net/okloeten/archive/2006/07/09/Hierarchical-Linq-Queries.aspx。

但我倾向于同意Jon Skeet的观点。

Answer 4

@Tomalok，当我使用这个数据结构运行你的代码时，我得到了两个节点。

class Program
{
    static void Main(string[] args)
    {
        var foo = new List<Category>();

        // Example structure from Question
        var fail1 = new Category() { Name = "test1" };
        var fail2 = new Category() { Name = "test2", ParentCategory = fail1 };
        var fail3 = new Category() { Name = "test3", ParentCategory = fail1 };
        var fail4 = new Category() { Name = "test4"};
        var fail5 = new Category() { Name = "test5", ParentCategory = fail4 };
        var fail6 = new Category() { Name = "test6", ParentCategory = fail4 };
        var fail7 = new Category() { Name = "test7", ParentCategory = fail4 };

        foo.Add(fail1);
        foo.Add(fail4);

        recurseCategories(ref foo, null, 0);

    }

    static void recurseCategories(ref List<Category> cl, Category start, int level)
    {
        foreach (Category child in cl)
        {
            if (child.ParentCategory == start)
            {
                Console.WriteLine(new String(   , level) + child.Name);
                recurseCategories(ref cl, child, level + 1);
            }
        }
    }

    public class Category
    {
        public string Name { get; set; }
        public Category ParentCategory { get; set; }
    }

}

输出。

test1
test4

输出应该是：

test1
   test 2
   test 3
test 4
   test 5
   test 6
   test 7

这是因为共享相同父节点的子节点之间没有关系。

友情链接