title: Joins Tables & Rails
body: <p>I have events and users/teams.</p>
  
  <pre><code>class Event
    has_many :users, :through =&gt; :registrations
  end
  class User
    has_many :events, :through =&gt; :registrations
  end
  class Registration
    belongs_to :users
    belongs_to :events
  end
  </code></pre>
  
  <p>When I register a user, I'm connecting them to the event like so:</p>
  
  <pre><code>@event.users &lt;&lt; @user
  </code></pre>
  
  <p>Does this implicitly create the Registration object for the user/event?  I've put a :goal_amount column in my Registration migration, and I would like to be able to set the :goal_amount when the Registration is created.  Do I need to explicitly create a Registration (ie: <code>Registration.create(:user_id =&gt; @user.id, :event_id =&gt; @event.id, :goal_amount =&gt; params[:goal_amount])</code> to make this happen?</p>