Linq group by element and a sub element

Structure is basically like this:

Master:

  Id 
  DocNo
  Laws[]

Laws is as follows:

LawNo
Id

I want to group by DocNo and LawNo
expected dictionary keys is:

{DocNo, LawNo}

And the value is

Master

I tried this but key is not like the expected

master.GroupBy(x => new {x.DocNo, _LawNo = x.Laws.Select(y => y.LawNo).Distinct()});

Thanks

>Solution :

If I understand correctly, you can try to use SelectMany before using GroupBy, SelectMany let LawNo flatten as DocNo

master.SelectMany(x=>x.Laws,(x,y)=>new{x.DocNo,y.LawNo})
      .GroupBy(x=> new {x.DocNo,x.LawNo});