linq - parent/child query to select only lowest level

Question

Given a common parent/child table:

Table A
Column Id int
Column Parent_Id int
Column Description text

I would like to only get the nodes that does not have any child nodes.

1,null,"PARENT A"
2,null,"PARENT B",
3,null,"PARENT C", 
100,1,"CHILD A1",
101,1,"CHILD A2",
102,2,"CHILD B1"

So for my resultset I would like to only get:

Parent C (as it does not have any child elements), and child A1, B2, B1.

score 1 · Accepted Answer · answered Aug 05 '12 at 14:06

1

You don't say what exactly you are querying with LINQ, but the general idea is

var leafNodes = nodes.Where(n => nodes.Count(n1 => n1.Parent_Id == n.Id) == 0);

answered Aug 05 '12 at 14:06

Jon

score 1 · Answer 2 · edited May 23 '17 at 10:24

1

You might wanna prefer Any() method instead of Count() == 0. See Which method performs better: .Any() vs .Count() > 0?

var itemsWithoutChildren = nodes.Where(item=>!nodes.Any(innerItem=>innerItem.Parent_Id==item.Id))

edited May 23 '17 at 10:24

Community

answered Aug 05 '12 at 14:07

M. Mennan Kara

2 Answers2