title: Shouldn't Building An Association Complete The Inverse Relationship?
body: <p>I was surprised to find that, given:</p>
  
  <pre><code>class Foo
    has_many :bars
    attr_accessible :baz
  end
  class Bar
    belongs_to :foo, inverse_of: :foo
  end
  </code></pre>
  
  <p>Then doing this:</p>
  
  <pre><code>new_bar = foo.bars.build params
  puts new_bar.foo.baz
  </code></pre>
  
  <p>Issues a call to the database to fetch foo.  Whaaa?</p>
  
  <p>You can prevent it by completing the inverse relation yourself:</p>
  
  <pre><code>new_bar.foo = foo
  </code></pre>
  
  <p>Am I doing something wrong? Is there any good reason that <code>#build</code>, knowing everything about both sides of the relation, should not compelte it?</p>