How to add multiselect for has_many through relationship in activeadmin form

Question

I have two models Degree and College connected many_to_many connection via Discipline table.

class Degree < ActiveRecord::Base
  has_many :disciplines
  has_many :colleges, :through => :disciplines
end 

class Discipline < ActiveRecord::Base
  belongs_to :college
  belongs_to :degree
end


class College < ActiveRecord::Base
  has_many :disciplines
  has_many :degrees, :through => :disciplines
end

I want to display multiple select (or checkboxes) with a degrees on the college new/update forms. How to do that?

Answer 1

In the College ActiveAdmin resource you can use the has_many method in the form block:

ActiveAdmin.register College do
    #...

    form do
      #...
      f.has_many :disciplines do |df|
        df.input :degree
      end
      #...
    end
    #...
end

This will be a multiselect select input by default. Find out more: https://github.com/activeadmin/activeadmin/blob/master/docs/5-forms.md#nested-resources