How to express a NOT IN query with ActiveRecord/Rails?

Question

I'm hoping there is a easy solution that doesn't involve find_by_sql, if not then I guess that will have to work.

I found this article which references this:

Topic.find(:all, :conditions => { :forum_id => @forums.map(&:id) })

which is the same as

SELECT * FROM topics WHERE forum_id IN (<@forum ids>)

I am wondering if there is a way to do NOT IN with that, like:

SELECT * FROM topics WHERE forum_id NOT IN (<@forum ids>)

Answer 1

Rails 4+:

Article.where.not(title: ['Rails 3', 'Rails 5']) 

Rails 3:

Topic.where('id NOT IN (?)', Array.wrap(actions))

Where actions is an array with: [1,2,3,4,5]