多级分层数据排序C＃

Question

我有一个实体：在数据库

public class Document 
{ 
    public int id; 
    public int? ParentId; 
    public string name; 
} 

和数据：

id | ParentId | name 
----------------------- 
1 |   | fruits 
2 |   | vegetables 
3 |  2  | tomatoes 
4 |  1  | apples 
5 |  4  | golden apples 
6 |  4  | red apples 

或者，如C＃：

var documents = new[] 
{ 
    new Document() { id = 1, ParentId = null, name = "fruits" }, 
    new Document() { id = 2, ParentId = null, name = "vegetables" }, 
    new Document() { id = 3, ParentId = 2, name = "tomatoes" }, 
    new Document() { id = 4, ParentId = 1, name = "apples" }, 
    new Document() { id = 5, ParentId = 4, name = "golden apples" }, 
    new Document() { id = 6, ParentId = 4, name = "red apples" }, 
}; 

我需要得到：

id | ParentId | name 
----------------------- 
1 |   | fruits 
4 |  1  | apples 
5 |  4  | golden apples 
6 |  4  | red apples 
2 |   | vegetables 
3 |  2  | tomatoes 

我如何在c＃中快速排序分层数据？

Answer 1

因此，考虑到：

public class Document 
{ 
    public int id; 
    public int? ParentId; 
    public string name; 
} 

和：

var documents = new[] 
{ 
    new Document() { id = 1, ParentId = null, name = "fruits" }, 
    new Document() { id = 2, ParentId = null, name = "vegetables" }, 
    new Document() { id = 3, ParentId = 2, name = "tomatoes" }, 
    new Document() { id = 4, ParentId = 1, name = "apples" }, 
    new Document() { id = 5, ParentId = 4, name = "golden apples" }, 
    new Document() { id = 6, ParentId = 4, name = "red apples" }, 
}; 

然后这个工程：

var lookup = documents.ToLookup(x => x.ParentId); 

Func<int?, IEnumerable<Document>> heirarchySort = null; 
heirarchySort = pid => 
    lookup[pid].SelectMany(x => new[] { x }.Concat(heirarchySort(x.id))); 

IEnumerable<Document> sorted = heirarchySort(null); 

它给你：