Question

I need to collect all authors in a tree like:

parent
|
+- child #1
|
+- child #1
|  |
|  +- grand child #1
|  |
|  +- grand child #2
|
+- child #2
...

(The origin post can have n childs and every child can also have m childs. Maximum depth from origin post is 2: Post – Child – Grandchild)

What is the best approach in Ruby on Rails to collect all authors (post belongs_to author)? My current approach is the following, but it seems not really performant:

def all_authors_in(post)
  @authors = Array.new
  @authors << post.author

  post.children.each do |child|
    @authors << child.author
    child.children.each do |grandchild| 
      @authors << grandchild.author
    end
  end

  @authors.map{|u| u.id}.uniq
end

Some code from the model:

class Post < ActiveRecord::Base
  belongs_to :parent, class_name: 'Post'
  has_many :children, foreign_key: :parent_id, class_name: 'Post', :dependent => :destroy
#...
end

Thanks

Answer 1

I assume you are using single table inheritance for your Post model, but you didn’t say if you rolled your own version. I’d recommend to use the ancestry gem. Then you could do something simple like this:

@authors = post.subtree.collect(&:author).uniq