如何查找特定类别 id c# 的分层树最后一个节点

Question

        List<Categories> categories = new List<Categories>
        {
            new Categories { CatID = 1, CatName = "Computer, IT & Networking"},
            new Categories { CatID = 2, CatName = "Computer & Servers"},
            new Categories { CatID = 3, CatName = "Desktop PCs"},
            new Categories { CatID = 4, CatName = "Servers"},
            new Categories { CatID = 5, CatName = "Computer Parts & Components"},
            new Categories { CatID = 6, CatName = "Harddrive"},
            new Categories { CatID = 7, CatName = "CPUs"},
            new Categories { CatID = 8, CatName = "Electronics"},
            new Categories { CatID = 9, CatName = "Furniture"},
            new Categories { CatID = 10, CatName = "RAM"},
            new Categories { CatID = 11, CatName = "Harddrive"},
            new Categories { CatID = 12, CatName = "Workbooks"},
            new Categories { CatID = 13, CatName = "IBM Desktop"},
            new Categories { CatID = 14, CatName = "HP Desktop"}
        };

        List<CategoriesMapping> categoriesMapping = new List<CategoriesMapping>
        {
            new CategoriesMapping { CategoriesMappingID = 1, CatID = 1, MapCatID = 2},
            new CategoriesMapping { CategoriesMappingID = 2, CatID = 1, MapCatID = 5},
            new CategoriesMapping { CategoriesMappingID = 3, CatID = 2, MapCatID = 3},
            new CategoriesMapping { CategoriesMappingID = 4, CatID = 2, MapCatID = 4},
            new CategoriesMapping { CategoriesMappingID = 5, CatID = 5, MapCatID = 6},
            new CategoriesMapping { CategoriesMappingID = 6, CatID = 5, MapCatID = 7},
            new CategoriesMapping { CategoriesMappingID = 7, CatID = 5, MapCatID = 10},
            new CategoriesMapping { CategoriesMappingID = 8, CatID = 5, MapCatID = 11},
            new CategoriesMapping { CategoriesMappingID = 9, CatID = 2, MapCatID = 12},
            new CategoriesMapping { CategoriesMappingID = 10, CatID = 3, MapCatID = 13},
            new CategoriesMapping { CategoriesMappingID = 11, CatID = 3, MapCatID = 14}
        };

如何获取特定 CatID 的最后一个节点，例如在上面的代码中，如果我选择 CatID = 2，它应该只带回 CatID 4、12、13、14。它不应该返回其子类别 CatID 3，因为它也有 13 和 14 的节点。相反，它只返回 CatID 3 的子节点。

Answer 1

我假设您正在尝试使用 linq 魔法解决此问题。不幸的是，在this answer by Jon Skeet，你可以看到它很不方便。

你可以试试like this，但它会变得相当昂贵。

我的建议是创建一个新函数，例如

   public List<int> GetNoDescendateCategoriesCategoryId(int categoryId) {
       List<int> newCategories = new List<int>();
       List<int> childCategories = this.categoriesMapping.Where(m => m.CatID == categoryId).Select(x=> x.MapCatID).ToList();

       if(childCategories.Count == 0) {
          return new List<int>() {categoryId};
       }
       foreach (int catId in childCategories ) {
          newCategories.AddRange(GetNoDescendateCategoriesCategoryId(catId));
       }
       return newCategories;
   }

你可以查看https://dotnetfiddle.net/1IbjOf这个例子。

Answer 2

由于这是一个递归调用，我不认为 LINQ 是最好的方法。拥有一个简单的迭代或递归函数就可以完成这项工作。

    public IEnumerable<int> ExtractSubcategories(int categoryId)
    {
        var categories = new List<int> {categoryId};
        var subCategories = new List<int>();

        while (categories.Count > 0)
        {
            // categories will store the categories to check
            int cat = categories[0];
            categories.RemoveAt(0);

            // checking the mapped categories
            var mapped = categoriesMapping.Where(x => x.CatID == cat)
                                          .Select(x => x.MapCatID)
                                          .ToList();
            if (mapped.Count > 0) 
            {
                // there are mapped categories,
                // thus we look for their children
                categories.AddRange(mapped);
            }
            else 
            {
                // there are no mapped categories,
                // this category is a child, we add it to the result
                subCategories.Add(cat);
            }
        }

        return subCategories;
    }


    [Test]
    public void Test() => 
        CollectionAssert.AreEquivalent(ExtractSubcategories(2), new[] {4, 12, 13, 14});

Answer 3

你可以试试下面的，

public class A {

    public List<int> result = new List<int>();

    public static List<CategoriesMapping> categoriesMapping = new List<CategoriesMapping> {
        //your data
    };

    public List<int> GetChildren(int input) {
        var res = GetInnerChildren(input);
        if (res.Count == 0)
            result.Add(input);

        foreach (var item in res) {
            if (categoriesMapping.Count(x => x.CatID == item) == 0) {
                result.Add(item);
            }
            else {
                var childs = GetInnerChildren(item);
                foreach (var item2 in childs) {
                    GetChildren(item2);
                }
            }
        }
        result.Sort();
        return result;
    }

    public List<int> GetInnerChildren(int input) {
        return categoriesMapping.Where(x => x.CatID == input).Select(x => x.MapCatID).ToList() ?? new List<int>();
    }

}

您的 CategoriesMapping 模型，

public class CategoriesMapping {
    public int CategoriesMappingID { get; set; }
    public int CatID { get; set; }
    public int MapCatID { get; set; }
}

GetChildren 根据需要返回所需的输出

GetChildren(2) => 返回 4,12,13,14