Question

我希望输出像

Test Genre1/
Test Genre2/
Test Genre3/Test genre1               //(Bcoz id 1 as Test Genre1)
Test Genre4/Test genre2               //(Bcoz id 2 as Test Genre2)
Test genre1/Test Test genre3/Genre5   //(Bcoz id 3 as Test Genre3)

它应该是id中parent id和Linq的组合。

任何帮助将不胜感激......

Answer 1

您可以尝试返回在实体类上定义的IEnumerable的递归方法：

public class Genre
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int? ParentId { get; set; }

    public IEnumerable<Genre> GetSelfAndAncestors(IEnumerable<Genre> items)
    {
        yield return this;

        if (ParentId.HasValue)
        {
            var parent = items.First(x => x.Id == ParentId.Value);

            foreach (var ancestor in parent.GetSelfAndAncestors(items))
            {
                yield return ancestor;
            }
        }
    }
}

用法：

var genres = new[]
{
    new Genre {Id = 1, Name = "Test Genre 1", ParentId = null},
    new Genre {Id = 2, Name = "Test Genre 2", ParentId = null},
    new Genre {Id = 3, Name = "Test Genre 3", ParentId = 1},
    new Genre {Id = 4, Name = "Test Genre 4", ParentId = 2},
    new Genre {Id = 5, Name = "Test Genre 5", ParentId = 3}
};

foreach (var genre in genres)
{
    var path = genre.GetSelfAndAncestors(genres);
    Console.WriteLine(String.Join("/", path.Select(x => x.Name)));
}

如果树很深，您可能会发现将此实现与非IEnumerable实施相比有显着的性能影响。

Answer 2

给定一个递归调用的方法

将名称添加到字符串
以任何现有父

private static string SelectGenreName(IEnumerable<Genre> all, Genre g)
{
    var s = g.Name + '/';
    if(g.ParentId.HasValue){
        s += SelectGenreName(all, all.Single(x => x.Id == g.ParentId.Value));   
    }
    return s;
}

获得合理结果的代码*非常简单：
_{*明智的结果;您的上一个示例与之前的示例相反。上面的示例按照前四个示例给出了结果。即Child/Parent/Grandparent}

var genres = new[]
{
    new Genre {Id = 1, Name = "Test Genre 1", ParentId = null},
    new Genre {Id = 2, Name = "Test Genre 2", ParentId = null},
    new Genre {Id = 3, Name = "Test Genre 3", ParentId = 1},
    new Genre {Id = 4, Name = "Test Genre 4", ParentId = 2},
    new Genre {Id = 5, Name = "Test Genre 5", ParentId = 3}
};

var result = genres.Select(g => SelectGenreName(genres,g));

foreach(var r in result)
    Console.WriteLine(r);

实例：http://rextester.com/MXQUH43732

Answer 3

创建一个递归函数并在你的linq中使用该函数。像这样的东西。

//Recursive method
 private static string GetParentPath( IEnumerable<Item> items , Item item )
    {
        if (item.ParentId.HasValue)
        {
            return GetParentPath(items, items.First(i => i.Id == item.ParentId)) + "/" + item.GenreName;
        }

        return item.GenreName;
    }



var items = new Item[]
        {
            new Item {Id = 1, GenreName = "Test Genre 1", ParentId = null},
            new Item {Id = 2, GenreName = "Test Genre 2", ParentId = null},
            new Item {Id = 3, GenreName = "Test Genre 3", ParentId = 1},
            new Item {Id = 4, GenreName = "Test Genre 4", ParentId = 2},
            new Item {Id = 5, GenreName = "Test Genre 5", ParentId = 3}
        };



 // Linq query
        var result = from child in items
                  select new { Path = GetParentPath(items, child) };



    //Class used in example
 public class Item
    {
        public int Id { get; set; }

        public string GenreName { get; set; }

        public int? ParentId { get; set; }
    }

加入Linq的一栏记录？

3 个答案: