LINQ的嵌套的內部聯接

我想參加下表LINQ的嵌套的內部聯接

1. B_Book[1st Table] 
     -B_BID (Book ID)(PK) 
     -B_Name 
     -B_CategroyID (FK) 
2. BI_BookInstance [2nd Table] 
     -BI_IID(Instance ID) 
     -BI_BID (FK) 
     -BI_Price 
3. BC_BookCategory [3rd Table] 
     -BC_CategoryID (PK) 
     -BC_CategoryName

首先加入B_Book和BI_BookInstance再加入這些都與BookCategory的結果。（1日加入）[B_BID等於BI_BID] （第二嵌套加入）[1的結果加入B_CategoryID等於BC_CategoryID]

編輯

SQL會像下面這樣：

SELECT * FROM 
    (SELECT * FROM B_Book b JOIN BI_BookInstance bi on b.B_BID = bi.BI_BID) as t1 
    JOIN BC_BookCategoryID bc on bc.BC_CategoryID = t1.B_CategoryID

來源

2012-07-07 Zeb-ur-Rehman

我假設內部聯接（你的FKs不爲空），所以我想這樣的查詢：

var ctx = new YourEntities(); 

    var query = from b in ctx.B_Book 
       from bi in ctx.BI_BookInstance 
       from bc in ctx.BC_BookCategory 
       where b.B_BID == bi.BI_BID && b.B_CategoryID == bc.BC_CategoryID 
       select new 
       { 
        BInstID = bi.BI_IID, 
        BName = b.B_Name, 
        BPrice = bi.BI_Price, 
        BCategory = bc.BC_CategoryName 
       }; 

    foreach (var item in query) 
    { 
     Console.WriteLine(item.BInstID); 
     Console.WriteLine(item.BName); 
     Console.WriteLine(item.BPrice); 
     Console.WriteLine(item.BCategory); 
     Console.WriteLine(""); 
    }

來源

2012-07-07 17:53:01

什麼匹配你在LINQ中的查詢將是以下（你會注意到與SQL的相似性）。我還包含有關如何重命名字段一些例子返回，如價格或類別名稱：

var results = from b in B_Book 
    join bi in BI_BookInstance 
    on b.B_BID equals bi.BI_BID 
    join bc in BC_BookCategory 
    on b.B_CategoryID equals bc.BC_CategoryID 
    select new 
     { 
     // put in whatever fields you want returned here: 
    b.B_BID, 
    b.B_CategoryID, 
    b.B_Name, 
    bi.BI_BID, 
    bi.BI_IID, 
    Price = bi.BI_Price, 
    bc.BC_CategoryID, 
    CategoryName = bc.BC_CategoryName 
     };

來源

2012-07-08 18:53:37

你可以做到這一點沒有明確使用LINQ的連接語句，前提是導航性能很到位：

from b in ctx.B_Book 
from bi in b.BookInstances 
select new { b.Property1, bi.Property2, b.BookCategory.Name }

來源

2012-07-10 10:19:52

LINQ的嵌套的內部聯接

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