2

我找不到或想出一个通用且优雅的算法来让我填充树状结构。最简单的例子是博客存档：我有一堆可以按日期选择和排序的记录。我想要一棵树，其中年份可能是最高级别，几个月是下一个级别，而实际的帖子标题又是下一个。

到目前为止，我已经想出了一个可行的简单直接实现，但我确信可以使用 LINQ 等进行改进。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发生了变化，然后添加相应的树节点。“BlogEntry”是一个类，它同时引用了父级和子级，后来用于生成 HTML。

我欢迎有关改进算法的建议！

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;
    }
}
4

2 回答 2

4

我创建了一个测试示例，以检查逻辑的正确性。我认为这就是你所需要的。

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;        
   }
}
于 2012-12-15T11:52:34.710 回答
1

使用链接Playing with Linq grouping: GroupByMany ? 如何使用 LINQ 对数据进行分层分组？

我首先将我的代码重构为

解决方案 1

var results = from allPosts in db.Posts.OrderBy(p => p.DateCreated)
        group allPosts by allPosts.DateCreated.Year into postsByYear

        select new
        {
            postsByYear.Key,
            SubGroups = from yearLevelPosts in postsByYear
                        group yearLevelPosts by yearLevelPosts.DateCreated.Month into postsByMonth
                        select new
                        {
                            postsByMonth.Key,
                            SubGroups = from monthLevelPosts in postsByMonth
                                           group monthLevelPosts by monthLevelPosts.Title into post
                                           select post
                        }
        };

foreach (var yearPosts in results)
{
    //create "year-level" item
    var year = new BlogEntry { Name = yearPosts.Key.ToString().ToLink(string.Empty) };
    entries.Add(year);
    foreach (var monthPosts in yearPosts.SubGroups)
    {
            //create "month-level" item
        var month = new BlogEntry { Name = new DateTime(2000, (int)monthPosts.Key, 1).ToString("MMMM").ToLink(string.Empty), Parent = year };
        year.Children.Add(month);
        foreach (var postEntry in monthPosts.SubGroups)
        {
            //create "blog entry level" item
            var post = postEntry.First() as Post;
            var blogEntry = new BlogEntry { Name = post.Title.ToLink("/Post/" + post.PostID + "/" + post.Title.ToSeoUrl()), Parent = month };
            month.Children.Add(blogEntry);                       
        }
    }
}

然后变成更通用的

解决方案 2

var results = db.Posts.OrderBy(p => p.DateCreated).GroupByMany(p => p.DateCreated.Year, p => p.DateCreated.Month);

foreach (var yearPosts in results)
{
    //create "year-level" item
    var year = new BlogEntry { Name = yearPosts.Key.ToString().ToLink(string.Empty) };
    entries.Add(year);

    foreach (var monthPosts in yearPosts.SubGroups)
    {
            //create "month-level" item
        var month = new BlogEntry { Name = new DateTime(2000, (int)monthPosts.Key, 1).ToString("MMMM").ToLink(string.Empty), Parent = year };
        year.Children.Add(month);

        foreach (var postEntry in monthPosts.Items)
        {
            //create "blog entry level" item
            var post = postEntry as Post;
            var blogEntry = new BlogEntry { Name = post.Title.ToLink("/Post/" + post.PostID + "/" + post.Title.ToSeoUrl()), Parent = month };
            month.Children.Add(blogEntry);
        }
    }
}

................................................

public static class MyEnumerableExtensions
{
    public static IEnumerable<GroupResult> GroupByMany<TElement>(
        this IEnumerable<TElement> elements,
        params Func<TElement, object>[] groupSelectors)
    {
        if (groupSelectors.Length > 0)
        {
            var selector = groupSelectors.First();

            //reduce the list recursively until zero
            var nextSelectors = groupSelectors.Skip(1).ToArray();
            return
                elements.GroupBy(selector).Select(
                    g => new GroupResult
                    {
                        Key = g.Key,
                        Items = g,
                        SubGroups = g.GroupByMany(nextSelectors)
                    });
        }
        else
            return null;
    }
}

public class GroupResult
{
    public object Key { get; set; }
    public IEnumerable Items { get; set; }
    public IEnumerable<GroupResult> SubGroups { get; set; }
}
于 2012-12-15T12:58:35.100 回答