title: SQLAlchemy: eager loading of more than one relationship
body: <p>I want to query this structure:</p>
  
  <pre><code>A -&gt; B
  B -&gt; C
  B -&gt; D
  </code></pre>
  
  <p>what's the syntax to do this with the Load interface, the documentation is not very clear on this (<a href="http://docs.sqlalchemy.org/en/latest/orm/loading_relationships.html#sqlalchemy.orm.joinedload">http://docs.sqlalchemy.org/en/latest/orm/loading_relationships.html#sqlalchemy.orm.joinedload</a>). All I see is how to do:</p>
  
  <pre><code>A -&gt; B
  B -&gt; C
  C -&gt; D
  </code></pre>
  
  <p>Given the query:</p>
  
  <pre><code>query(A).options(joinedload(A.b).joinedload(B.c))
  </code></pre>
  
  <p>How do I go backward in the chain to specify the second relationship on B (B.d)?</p>