Linq中使用Left Join rught join

　　准備一些測試數據，如下：

 

           use Test 
          
Create table Student( 
          
ID int identity(1,1) primary key, 
          
[Name] nvarchar(50) not null 
          
) 
          
 
          
Create Table Book( 
          
ID int identity(1,1) primary key, 
          
[Name] nvarchar(50)not null, 
          
StudentID int not null 
          
) 
          
 
          
insert into Student values('張三') 
          
insert into Student values('李四') 
          
insert into Student values('王五') 
          
select * from student 
          
 
          
--張三借的書 
          
insert into Book values('紅樓',1) 
          
insert into Book values('大話紅樓',1) 
          
 
          
--李四借的書 
          
insert into Book values('三國',2) 
          
 
          
--王五沒借書 
          
 
          
--一本錯誤的記錄 
          
insert into Book values('錯誤時怎樣練成的',111) 
          
 
          
--左連接 
          
select s.name,b.name from student as s 
          
left join Book as b on s.id=b.studentid 
          
 
          
--右連接 
          
select s.name,b.name from student as s 
          
right join Book as b on s.id=b.studentid 
         

 

要用Linq實現左連接，寫法如下

 

           DataClasses1DataContext db = new DataClasses1DataContext(); 
          
 var leftJoinSql = from student in db.Student 
          
 join book in db.Book on student.ID equals book.StudentID into temp 
          
 from tt in temp.DefaultIfEmpty() 
          
 select new 
          
 { 
          
 sname= student.Name, 
          
 bname = tt==null?"":tt.Name//這里主要第二個集合有可能為空。需要判斷 
          
 }; 
         

 

 

 

 

用Linq實現右連接，寫法如下

 

 

           DataClasses1DataContext db=new DataClasses1DataContext(); 
          
 var rightJoinSql = from book in db.Book 
          
 join stu in db.Student on book.StudentID equals stu.ID into joinTemp 
          
 from tmp in joinTemp.DefaultIfEmpty() 
          
 select new { 
          
 sname=tmp==null?"":tmp.Name, 
          
 bname=book.Name 
          
 
          
 }; 
         

 

 

參考資料：http://developer.51cto.com/art/200909/152189.htm

http://hi.baidu.com/thinsoft/blog/item/83fb1e9089cc7186a877a4b1.html

http://apps.hi.baidu.com/share/detail/12540006

http://www.winu.cn/space-14160-do-blog-id-25172.html