c# - 生成结构以填充树的查询或算法(C#、LINQ)

Question

我找不到或想出一个通用且优雅的算法来填充树状结构。最简单的例子是博客存档:我有一堆记录，可以按日期选择和排序。我想要一棵树，其中年份可能是最高级别，月份是下一级，实际帖子标题是下一个。

到目前为止，我想出了一个简单直接的可行实现，但我确信可以使用 LINQ 等改进它。在这里，我只是按日期对记录进行排序，并反复检查年份或月份是否已更改，并相应地添加树节点。“BlogEntry”是一个同时引用父项和子项的类，稍后用于生成 HTML。

我欢迎提出改进算法的建议!

IEnumerable<Post> posts = db.Posts.OrderBy(p => p.DateCreated);
var topPost = posts.First();

int curYear = topPost.DateCreated.Year;
int curMonth = topPost.DateCreated.Month;

//create first "year-level" item
var topYear = new BlogEntry { Name = topPost.DateCreated.Year.ToString().ToLink(string.Empty) };
entries.Add(topYear);
var currentYear = topYear;

var topMonth = new BlogEntry { Name = topPost.DateCreated.ToString("MMMM").ToLink(string.Empty), Parent = currentYear };
currentYear.Children.Add(topMonth);
var currentMonth = topMonth;

foreach (var post in posts)
{
    if(post.DateCreated.Year == curYear)
    {
        if (post.DateCreated.Month != curMonth)
        {
            //create "month-level" item
            var month = new BlogEntry { Name = post.DateCreated.ToString("MMMM").ToLink(string.Empty), Parent = currentYear };
            currentYear.Children.Add(month);
            currentMonth = month;

            curMonth = post.DateCreated.Month;
        }

        //create "blog entry level" item
        var blogEntry = new BlogEntry { Name = post.Title.ToLink("/Post/" + post.PostID + "/" + post.Title.ToSeoUrl() ), Parent = currentMonth };
        currentMonth.Children.Add(blogEntry);
    }
    else
    {
        //create "year-level" item
        var year = new BlogEntry { Name = post.DateCreated.Year.ToString().ToLink(string.Empty) };
        entries.Add(year);
        currentYear = year;

        curMonth = post.DateCreated.Month;
        curYear = post.DateCreated.Year;
    }
}

Answer 1

我创建了一个测试示例，以检查逻辑的正确性。我认为这就是您所需要的。

public class BlogEntyTreeItem
{
   public string Text { set; get; }
   public string URL { set; get; }
   public List<BlogEntyTreeItem> Children { set; get; }

   public List<BlogEntyTreeItem> GetTree()
   {
       NWDataContext db = new NWDataContext();
       var p = db.Posts.ToList();

       var list = p.GroupBy(g => g.DateCreated.Year).Select(g => new BlogEntyTreeItem
       {
           Text = g.Key.ToString(),
           Children = g.GroupBy(g1 => g1.DateCreated.ToString("MMMM")).Select(g1 => new BlogEntyTreeItem
           {
               Text = g1.Key,
               Children = g1.Select(i => new BlogEntyTreeItem { Text = i.Name }).ToList()
           }).ToList()
       }).ToList();

       return list;        
   }
}