If your not returning ruby primitives and other objects that know how to respond to #as_json from #as_jons - Your doing it wrong.

gistfile1.rb

class User < ActiveRecord::Base  
  has_many :columns
  def as_json(options={})
    attributes.slice(:id, :email, :uuid).merge(:columns => columns)
  end
end

class Column < ActiveRecord::Base
  belongs_to :user
  has_many :boxes
  def as_json(options=nil)
    attributes.slice(*JSON_ATTRS).merge(:boxes => boxes)
  end
end

class Box < ActiveRecord::Base
  belongs_to :column
  has_many :bookmarks
  def as_json(options=nil)
    attributes.slice(:id, :column_id, :title, :style, :collapsed, :position).merge(:bookmarks => bookmarks)
  end
end

class Bookmark < ActiveRecord::Base
  belongs_to :box
  def as_json(options=nil)
    attributes.slice(:id, :owner_id, :owner_type, :url, :name, :position)
  end
end