title: Outer Join with ORM mapping in SQLAlchemy
body: <p>I am using the ORM Mapping in SQLAlchemy 0.6.8.</p>
  
  <p>I have three tables (A, B and C), with no foreign keys between them.</p>
  
  <p>I am trying to join table A and B, and then left outer join that with C. I am expecting a named tuple, with fields A, B and C - with the C field sometimes set to None.)</p>
  
  <p>I can do the first join easily enough by just selecting both table.</p>
  
  <pre><code>(session.query(A, B)
      .filter(A.some_field = B.some_other_field))
  </code></pre>
  
  <p>That gets me a NamedTuple with fields A and B.</p>
  
  <p>I then add the outer join, to make it:</p>
  
  <pre><code>(session.query(A, B)
      .filter(A.some_field==B.some_other_field))
      .outerjoin((C, A.some_field==C.some_different_field))
  </code></pre>
  
  <p>The result still only has two tables. I can't access the other fields of C (even in the cases where they are present).</p>
  
  <p>What is the correct way to do an left outer join, to get access to the fields of the right-most table??</p>
  
  <p>I'd rather not fallback to the basic SQL if I could avoid it - I am trying to learn to take advantage of the ORM.</p>