title: Issue with SqlAlchemy - "Parent instance <SomeClass> is not bound to a Session; lazy load operation..."
body: <p>I have a small thrift server in python that I use do some fast lookups. The server queries mysql via SqlAlchemy on the first request and shoves all returned objects into a dictionary so on subsequent requests no DB call is needed. I just get the object from the dict and then call some of the object methods needed to give the proper response.</p>
  
  <p>Initially, everything is fine. However, after the server runs a while, I am getting this exception when accessing the sqlalchemy object methods:</p>
  
  <blockquote>
    <blockquote>
      <p>Parent instance  is not bound to a Session; lazy load operation of attribute 'rate' cannot proceed.</p>
    </blockquote>
  </blockquote>
  
  <p>Strange, because I set <code>eagerload('rate')</code>.</p>
  
  <p>I cannot really see a pattern to this behavior, it only affects some objects. However, once it does affect an object it will continue to do so on each request until I restart my python server.</p>
  
  <p>Any ideas?</p>