如何为包含自连接的多个连接编写LINQ

本文关键字：连接 LINQ 包含 自连接 | 更新日期: 2023-09-27 18:07:38

我试图将以下带有自连接的查询翻译为LINQ表达式。

select r2.* from depends d
  join request r on d.DESC =r.DESC
  join request r2 on d.ID=r2.ID
  and d.TYPE ='sometype'
where r.ID= 12345

我如何纠正以下LINQ查询以匹配上面正确的SQL查询?

var result = (from d in depends
            join r in request on d.DESC equals r.DESC
            join r2 in request on d.ID == r2.ID && d.TYPE == incomingType.ToString()
            where r.ID == incomingId
            select r2).AsEnumerable();

如何为包含自连接的多个连接编写LINQ

如果您的incomingType是固定的，为什么不简单地使用Where条款呢?

也有用于多个连接条件的语法，如下所示:

例如:

var result = (from d in depends
              where d.TYPE == incomingType.ToString()
              join r in request on
              new { ID = r.ID, desc = r.DESC }
              equals 
              new { ID = d.ID, desc = d.DESC }
              where r.ID == incomingId
              select r).AsEnumerable();

如果你的incomingType实际上不是固定的，并且它从depends表中获得它的值，你可以只添加第三个参数到连接条件，例如

var result = (from d in depends
              where d.TYPE == incomingType.ToString()
              join r in request on
              new { ID = r.ID, desc = r.DESC, type = r.someType1 }
              equals 
              new { ID = d.ID, desc = d.DESC, type = d.someType2 }
              where r.ID == incomingId
              select r).AsEnumerable();
相关文章：