add to collection_select dynamically

Question

I have 3 Models: Course, Unit and Plan. relations are like:

Course has_many units
Unit belongs_to course

Plan has_and_belongs_to_many units
Unit has_and_belongs_to_many plans

In the create_plan page, I have a collection_select to get units of my plan; but units don't have title,they use their course title. I want to show the course title in the collection_select. how can I do that?

Answer 1

Delegate title to the course

class Unit
  belongs_to course
  delegate :title, to: :course
end

<%= f.collection_select(:unit_id, Unit.all, :id, :title, prompt: true) %>