title: Rails (ActiveRecord) many to many table
body: <p>I have two models, Users and Groups. Each group can have many users and each user can be in many groups.</p>
  
  <p>I currently have something simple like:</p>
  
  <p>User:</p>
  
  <pre><code>has_many    :groups
  </code></pre>
  
  <p>Group:</p>
  
  <pre><code>has_many    :users
  </code></pre>
  
  <p>So I have a groups_users table which is just creating rows with group_id and user_id.
  I want to add another column to this, (which I have), the question is how do I access it from a model without using a custom SQL call? In the group model I can go self.users and in user I can go self.groups</p>
  
  <p>Is there a way to change the third column in this table from a user model?</p>
  
  <p>Sorry if this is confusing, please advise on this</p>