LINQ查询外部联接的父级和子级（嵌套）表

Question

I have three levels of tables "Directors", "Managers" and "Leaders" with one to many relationship between them.

I would like to bring All the rows from Directors, Managers and Leaders separately along with their children relationship.(maybe LeftOuterJoin)

For example Directors table have

DirectorID DirectorName

     1            Director1 

Managers

Manager ID Director ID Manager Name

  1              1                 Manager 1
  2              1                 Manager 2

Leaders

Leader ID Manager ID Leader Name

  1                 1              Leader 1  
  2                 1              Leader 2

I want the query to return

DirID DirectorName MgrID ManagerName LdrID LeaderName

1 Director1
1 Director1 1 Manager1
1 Director1 1 Manager1 1 Leader1
1 Director1 1 Manager1 2 Leader1
1 Director1 2 Manager2

My linq query only results 3 rows

DirID DirectorName MgrID ManagerName LdrID LeaderName

1 Director1 1 Manager1 1 Leader1
1 Director1 1 Manager1 2 Leader1
1 Director1 2 Manager2

             var query = from d in db.Directors
                        join m in db.Managers on d.DirectorID equals m.DirectorID into directorMgrGroup
                        from dmgr in directorMgrGroup.DefaultIfEmpty()
                        join l in db.Leaders on dmgr.ManagerID equals l.ManagerID into mgrLeaderGroup
                        from mlgr in mgrLeaderGroup.DefaultIfEmpty()

It feels like a small tweak. just can't get it right. can anyone please help me? Thank you.

Answer 1

It feels like a small tweak

Well, not exactly. The result format in SQL is produced by so called ROLLUP query which is not supported natively by LINQ. GroupJoin will gather the information needed, but flattening it the way you want is quite hard as you may see below (combinations of singe item array concatenating the group join groups). Check it out:

var query =
db.Directors.GroupJoin(db.Managers, director => director.DirectorId, manager => manager.DirectorId, (director, managerGroup) => new
{
    Id = director.DirectorID,
    Name = director.DirectorName,
    Managers = managerGroup.GroupJoin(db.Leaders, manager => manager.ManagerId, leader => leader.ManagerID, (manager, leaderGroup) => new
    {
        Id = manager.ManagerID,
        Name = manager.ManagerName,
        Leaders = leaderGroup.Select(leader => new
        {
            Id = leader.LeaderID,
            Name = leader.LeaderName
        })
    })
})
.SelectMany(director =>  
    new[] { new
    {
        DirID = director.Id, DirectorName = director.Name,
        MgrID = (int?)null, ManagerName = (string)null,
        LdrID = (int?)null, LeaderName = (string)null
    } }
    .Concat(director.Managers.SelectMany(manager => 
        new[] { new
        {
            DirID = director.Id, DirectorName = director.Name,
            MgrID = (int?)manager.Id, ManagerName = manager.Name,
            LdrID = (int?)null, LeaderName = (string)null
        } }
        .Concat(manager.Leaders.Select(leader => new
        {
            DirID = director.Id, DirectorName = director.Name,
            MgrID = (int?)manager.Id, ManagerName = manager.Name,
            LdrID = (int?)leader.Id, LeaderName = leader.Name
        }))
    ))
);

Answer 2

I would suggest you to write a SQL query, put it into a sql View and map it as an EF entity. This way you get this exeuced in the DB (it's still the fastest to run) and can still filter it in EF.

outer joins are always a pain in the ass with EF

Create View ViewMyShiningAss
Begin
 /* select the outer join shit */
end

Update the EF model

using(var ctx = new MyModelEntities())
{
    var x = ctx.ViewMyShiningAss.ToList();
}