title: missing attribute in activerecord
body: <p>I have models <code>Foo</code> and <code>Bar</code>. <code>Bar</code> has column <code>foo_id</code>. 
  When I call <code>Bar.foo_id</code> I get the error <code>missing attribute: foo_id</code></p>
  
  <p>Keep in mind that this is not an undefined method error and the column definitely is in the db. What are some common causes of this?</p>
  
  <p>Thanks</p>