Question

What would be the right (Rails) way to have one model with both a has_many and a has_one relationship? In my case, I want my Device model to keep track of both its current location and all of its previous locations.
This is my attempt and it is functional but is there a better way?

Models

class Location < ActiveRecord::Base
  belongs_to :device
end

class Device < ActiveRecord::Base
  has_many :locations # all previous locations
  belongs_to :location # current location
end

Answer 1

class Location < ActiveRecord::Base
  belongs_to :device
end

class Device < ActiveRecord::Base
  has_many  :locations

  def previous_locations
    self.locations.order('created_at asc').limit( self.locations.count-1)
  end

  def current_location # or last_location
    self.locations.order('created_at desc').limit(1)
  end

  # you may like to add this one
  def current_location= args
    args = Location.new args unless args.is_a? Location
    self.locations << args
  end
end

Note that all @device.locations, @device.previous_locations, and @device.current_location will return ActiveRecord::Relation