title: Trying to join two models, not sure what the appropriate active record association should be
body: <p>I have two models- Volunteer and Registration.</p>
  <p>Volunteers are more stable, but Registrants will come and go. I am trying to assign a new registration to a volunteer, by having a foreign key in my Registration model  for the volunteer_id.</p>
  <p>I've looked <a href="https://stackoverflow.com/questions/32201949/what-is-the-behaviour-of-create-join-table-of-activerecordmigration">here</a> and <a href="https://stackoverflow.com/questions/21083625/rails-joining-multiple-tables">here</a> and ended up creating a join table that includes the ids of both registrations and volunteers:</p>
  <pre><code>class CreateJoinTable &lt; ActiveRecord::Migration[5.0]
    def change
      create_join_table :registrations, :volunteers do |t|
        t.index [:registration_id, :volunteer_id], name: :reg_vol_index
        t.index [:volunteer_id, :registration_id], name: :vol_reg_index
      end
    end
  end
  </code></pre>
  <p>In my two models I'm not entirely sure what to list the associations as - I've read about has_many, belongs_to, and has_many_and_belongs_to- as well as t.reference.</p>
  <p>I'm only wanting to be able to assign a volunteer id to a registration.</p>
  <p>Can anyone help clarify what type of association is best?</p>
  <p>Thanks in advance!</p>