Linq 中Left join与 Group by一起使用

 直接看SQL语句：

  public  IList < StructureRootDTO >  GetRootStructureInfos()
        {
             using  (ETCDataContext etcDataContext  =   this .EtcDataContext)
            {
                var query  =
                       from item  in
                           (
                               from parent  in  etcDataContext.SYS_Structures
                                where  parent.ParentNode  ==   " root "
                               join child  in  etcDataContext.SYS_Structures
                               on parent.Name equals child.ParentNode into childAll
                               from childItem  in  childAll.DefaultIfEmpty()
                               select  new
                               {
                                   parent.ID,
                                   parent.Name,
                                   childItem.ParentNode
                               }
                           )
                       group item by item.Name into groupChild                      
                       select  new  StructureRootDTO
                       {
                           ID  =  groupChild.Max(o  =>  o.ID),
                           Name  =  groupChild.Max(o  =>  o.Name),
                           ChildParentNodeName  =  groupChild.Max(o  =>  o.ParentNode)
                       };
                 return  query.OrderBy(o  =>  o.ID).ToList();
            }
        }

 

生成query的SQL为：

 

SELECT   MAX ( [ t2 ] . [ ID ] )  AS   [ ID ] ,  MAX ( [ t2 ] . [ Name ] )  AS   [ Name ] ,  MAX ( [ t2 ] . [ value ] )  AS   [ ChildParentNodeName ]
FROM  (
     SELECT   [ t0 ] . [ ID ] ,  [ t0 ] . [ Name ] ,  [ t1 ] . [ ParentNode ]   AS   [ value ] ,  [ t0 ] . [ ParentNode ]
     FROM   [ dbo ] . [ SYS_Structure ]   AS   [ t0 ]
     LEFT   OUTER   JOIN   [ dbo ] . [ SYS_Structure ]   AS   [ t1 ]   ON   [ t0 ] . [ Name ]   =   [ t1 ] . [ ParentNode ]
    )  AS   [ t2 ]
WHERE   [ t2 ] . [ ParentNode ]   =   ' root '
GROUP   BY   [ t2 ] . [ Name ]