Question

That title probably doesn’t sound right, but forgive me, I’m learning Rails for the first time after ten years of windows development. Currently, I have a model named Drill that should contain two exercises. To accomplish this based on my current knowledge of Rails, I created a has_many association between the Drill and Exercise models…

class Drill < ActiveRecord::Base
  has_many :exercises, :dependent => :destroy
end

But I don’t want an open ended list of exercises, instead I’d like to have two references to a single Exercise object, one called left_drill and the other called right_drill. Based on the documentation, I’ve changed the code to this…

class Drill < ActiveRecord::Base
  has_one  :right_drill, :class => :exercise
  has_one  :left_drill, :class => :exercise
end

But I don’t know if that’s right and I’m having a hard time testing it because I don’t know how to adjust the Exercise model respectively. As of now, the Exercise model remains the same…

class Exercise < ActiveRecord::Base
  belongs_to :drill
end

Having a hard time figuring out how to accomplish this and, while I continue to read through the docs, I was hoping someone could give me a little direction.

Thanks so much for your wisdom!

Answer 1

What you have is correct, though typically the explicit class name is given as a string like so:

class Drill < ActiveRecord::Base
  has_one :left_drill, :class => "Exercise"
  has_one :right_drill, :class => "Exercise"
end

You can also easily access both drill objects like so, where my_drill is an instance of Drill:

my_drill.left_drill
my_drill.right_drill

You may wish to consider renaming them left_exercise and right_exercise to better reflect that they are an instance of the Exercise model, not the Drill model.