C# LINQ用方法语法怎么实现SQL中的left join 和 right join这种查询？

Question

C# LINQ用方法语法怎么实现SQL中的left join 和 right join这种查询？

Answer 1

//inner join
from a in StoreInCities
join b in CityInfo on a.CityId equals b.ID into c
select c

//left join   (right join只是顺序换一下)
from a in StoreInCities
join b in CityInfo on a.CityId equals b.ID into c
//DefaultIfEmpty()是为了达到左连接的目的，不使用DefaultIfEmpty()，相当于是inner join
from d in c.DefaultIfEmpty()
select d

//上面的left join等价于下面的方法语法
StoreInCities
   .GroupJoin (
      CityInfo, 
      a => a.CityId, 
      b => b.ID, 
      (a, c) => 
         new  
         {
            a = a, 
            c = c
         }
   )
   .SelectMany (
      temp0 => temp0.c.DefaultIfEmpty (), 
      (temp0, d) => d
   )


//推荐一个软件，sql，ling方法和ling表达式语法各种切换的软件（linqpad）

Answer 2

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Answer 3

GroupJoin

右连接就是把右表写在左边