在LINQ中订购自引用层次结构 [英] Ordering a self-referencing hierarchy in LINQ

问题描述

我有一个名为NavigationElement的类，看起来像这样

I have a class called NavigationElement that looks like this

public class NavigationElement
{
  public int Id { get; set; }
  public string Title { get; set; }
  public string Link { get; set; }
  public int SortOrder { get; set; }
  public bool Visible { get; set; }
  public int? ParentId { get; set; }

  public virtual ICollection<NavigationElement> Children { get; set; }
  public virtual NavigationElement Parent { get; set; }

  public NavigationElement()
  {
    Children = new List<NavigationElement>();
  }
}

如您所见，该类是自引用的.由此，我创建了一个带有下拉菜单(正在播放层次结构)的网站导航菜单.

As you can see, the class is self referencing. From that, I am creating a site navigation menu with drop downs (hierarchy in play).

我在订购物品方面很挣扎.我希望通过SortOrder属性对顶层项进行排序，但是其下的所有内容，我希望通过Title属性对按字母顺序进行排序.

I am struggling in the ordering of the items. I want the top-level items to be ordered by the SortOrder property, but everything underneath, I would like ordered alphabetically by the Title property.

这就是我到目前为止所做的原因.

Here is why I have done so far.

var orderedModel = unorderedModel.OrderBy(x => x.SortOrder).ThenBy(x => x.Children.OrderBy(y => y.Title).ThenBy(z => z.Children.OrderBy(a => a.Title))).ToList();

unorderedModel的类型为List<NavigationElementModel>.

这正在编译，但是运行代码时出现错误.错误提示:

This is compiling, but I get an error when I run the code. The error says:

至少一个对象必须实现IComparable.

At least one object must implement IComparable.

推荐答案

您应该对所有子元素进行递归并对其进行排序.

You should just go recursive through all children elements and sort it.

类似:

var ordered = unorderedModel.OrderBy(x=>x.SortOrder).ToList();
ordered.ForEach(OrderChildren);

public void OrderChildren(NavigationElement el)
{
    el.Children = el.Children.OrderBy(x => x.Title).ToList();
    if (el.Children != null)
    {
        foreach (var c in el.Children)
        {
            OrderChildren(c);
        }
    }
}

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