Question

I have models set up similar to this:

class Book < ActiveRecord::Base
  has_many :histories, as: :object
end

class Magazine < ActiveRecord::Base
  has_many :histories, as: :object
end

class Action < ActiveRecord::Base
  belongs_to :object, polymorphic: true

  default_scope order(:done_at)

  # a history contains an action and the time that action 
  # occurred on the object it belongs to
end

Now, I want to get a list of the 5 lastest actions that have occurred on all objects. So I can do something like:

Action.limit(5)

However, the problem is that if two actions have recently occurred on the same book, both actions will be retrieved. I want to only retrieve the lastest one. How do I achieve this?

Answer 1

Figured out that what I wanted was the group option. So I can do something like:

Action.group(:object_id).group(:object_type).limit(5)