Bad values for acts_as_nested_set?

I moved from acts_as_tree to acts_as_nested_set because I need the
all_children method.

I’ve seen an alternative way to add this method to acts_as_tree here:
http://www.chuckvose.com/articles/2006/05/24/recursive-children
But I’d prefer to use the more efficient way of acts_as_nested_set (and
not to have to revert to my old code).

Anyway, here’s my issue: if I already have a root1 element with lft:1
and rgt:4 (has one child) and add a new root2 (has one child also), it
is assigned lft:1 and rgt:4 also!

So if I ask for root2.all_children I also retrieve the child of root1!

My migration schema:

create_table “elements”, :force => true do |t|
t.column “name”, :string
t.column “category_id”, :integer
t.column “parent_id”, :integer
t.column “lft”, :integer
t.column “rgt”, :integer
t.column “created_at”, :datetime
end

Some code to reproduce the results:

root1 = Element.create(:name => “root1”)
root1.add_child(Element.create(:name => “root1child”)
root2 = Element.create(:name => “root2”)
root2.add_child(Element.create(:name => “root2child”)

Data view:

ID | PARENT_ID | LFT | RGT | NAME
1 | 0 | 1 | 4 | root1
2 | 1 | 2 | 3 | root1child
3 | 0 | 1 | 4 | root2
4 | 1 | 2 | 3 | root2child

Which produces this query when asking for root2.all_children:

SELECT * FROM keywords WHERE (1 = 1 AND (lft > 1) and (rgt < 4))

Baaaad!! I though it would be:

ID | PARENT | LEFT | RIGHT | DATA
1 | 0 | 1 | 4 | root1
2 | 1 | 2 | 3 | child1
1 | 0 | 5 | 8 | root2
2 | 1 | 6 | 7 | child1

And produce:

SELECT * FROM keywords WHERE (1 = 1 AND (lft > 5) and (rgt < 8))

Is this normal behavior for acts_as_nested_set or is there something
broke here?

Thank you for reading me!

Finally I found even smarter methods to add all_children support for
acts_as_tree, so I let down acts_as_nested_set (and efficiency) and
revert to acts_as_tree.

See descendants methods here:
http://blog.rapidred.com/articles/2006/06/08/ruby-working-with-trees
http://paste.lisp.org/display/9567

But these two methods return descendants plus self. I’d want to have a
method that returns really only descendants.

How can I do that?