title: Are there any reasons you might not want to have a foreign_key in an association?
body: <p>If you have </p>
  
  <pre><code>Parent
   has_many :children
  
  Child
  </code></pre>
  
  <p>Is there any reason a foreign key on Child (to Parent) and a corresponding <code>belongs_to :parent</code> might not be desirable?</p>
  
  <p>When, if ever, would you not want your Child to be able to access its parent?</p>