title: If and how to use the has_and_belongs_to_many association in ActiveRecord
body: <p>Trying to create a domain in which a user can create list of coffees and blends. A blend has many coffees and a coffee has many blends. This is what I have so far:</p>
  
  <pre><code>class User &lt; ActiveRecord::Base
    has_many :roasts
    has_many :blends, :through =&gt; :roasts
  
  class Roast &lt; ActiveRecord::Base
    belongs_to :user
    # TODO: associate roasts with blends
  
  class Blend &lt; ActiveRecord::Base
    # TODO: associate blends with roasts
  </code></pre>
  
  <p>How do I establish this relationship? Will I need a join table of some sort?</p>