在LINQ中创建两级层次结构

Question

I have two tables in SQL:

DOCUMENT
ID int
Description varchar(50)

DOCUMENTLINK
ParentID int
ChildID int

How do I return the hierarchy (only two levels are used) formed by these two tables as an object using LINQ?

The structure would be something like:

Parent1  
---------Child1  
---------Child2  
Parent2  
---------Child3  
Parent3  
Parent4  
---------Child2  
---------Child3  
Parent5  
---------Child1  
---------Child4
---------Child5

Answer 1

LINQ answer:

var tree = from top in nodes
           from middle in nodes
           from bottom in nodes
           where top.Id == middle.ParentId
           && middle.Id == bottom.Id
           select new
           {
               Top = top,
               Middle = middle,
               Bottom = bottom
           };

Answer 2

The SQL answer is:

SELECT *
FROM (Table1
INNER JOIN Table1 AS Table1_1 ON Table1.ParentID = Table1_1.ID)
INNER JOIN Table1 AS Table1_2 ON Table1_1.ParentID = Table1_2.ID;

Note, this will only show items that have all levels. To get childless parents included, change all the inner joins to left outer joins