title: rails 3 habtm delete only association
body: <pre><code>class Company
    has_and_belongs_to_many :users
  end
  
  class User
    has_and_belongs_to_many :companies
  end
  </code></pre>
  
  <p>when i delete a company, what's the best (recommended) way to delete ONLY the associations of the users from that company? (i mean not the actual users, only the associations)</p>