LINQ的 - 從鏈接的鏈接表中檢索值

Question

我有以下的模型和關係：

Table: Granddad 
GranddadID 
GranddadName 

Table: Father 
FatherID 
GranddadID 
FatherName 

Table: Son 
SonID 
FatherID 
SonName 

在爺爺控制器：

public ActionResult Edit(int tmpgranddadid) 
{ 
    var q = (from g in _e.Grandad 
      where g.GrandadID == tmpgranddadid 
      select g).FirstOrDefault(); 

    string son_name = q.Father.Son.SonName.ToString(); // <- is wrong, how to do this? 

    return View(q); 
} 

你如何檢索鏈接的鏈接表中的值？

謝謝

Answer 1

假設您的數據源看起來是這樣的：

public class SomeDataSource 
{ 
    public List<Granddad> Granddad; 
    public List<Father> Father; 
    public List<Son> Son; 
} 

並假設你實際上是一個爺爺那麼第一孫子後：

var firstGrandson = (from son in _e.Son 
       join father in _e.Father on son.FatherID equals father.FatherID 
       join granddad in _e.Granddad on father.GranddadID equals granddad.GranddadID 
       where granddad.GranddadID == tmpgranddadid 
       select son).FirstOrDefault(); 

if (firstGrandson == null) 
    throw new Exception("This granddad has no grandsons."); 

string son_name = firstGrandson.SonName; 

這是你需要的嗎？

Answer 2

退房加入：

http://www.hookedonlinq.com/JoinOperator.ashx

Answer 3

也許你想任何可能多的兒子？

q.Fathers.First().Sons.First().SonName.ToString(); 

要小心，因爲如果父親沒有兒子，First（）會拋出異常。這將處理這種情況：

string sonName = null; 
Father father = q.Fathers.FirstOrDefault(); 
if (father != null) { 
    Son son = father.Sons.FirstOrDefault(); 
    if (son != null) { 
     sonName = son.SonName.ToString(); 
    } 
}