Rails 3 - acts_as_nested_set

How do I install "acts_as_nested_set" in my Rails 3 app?

I want to be able to add a开发者_JAVA技巧cts_as_nested_set to my model

I also want to be able to use ROOT, like this...

article.comments.roots.order

Ideas?

You may want to take a look at Awesome Nested Set (at least some of its forks) and Nested Set on github. They provide acts_as_nested_set replacement for Rails 3.