title: AttributeError: 'unicode' object has no attribute '_sa_instance_state'
body: <p>I'm just learning how to use SQLAlchemy. I'm trying to do the following, but storing title and link in two separate tables:</p>
  
  <pre><code>temp = Submissions(title=u'Facebook Homepage', link=u'http://facebook.com')
  session.add(temp)
  session.flush()
  transaction.commit()
  </code></pre>
  
  <p>via:</p>
  
  <pre><code>class Links(Base):
      __tablename__ = 'links'
      id = Column(Integer, primary_key=True)
      link = Column(Text)
      created = Column(TIMESTAMP(), default=datetime.now())
  
      def __init__(self, link):
          self.link = link
  
  class Submissions(Base):
      __tablename__ = 'submissions'
      id = Column(Integer, primary_key=True)
      created = Column(TIMESTAMP(), default=datetime.now())
      title = Column(Text)
      link_id = Column(Integer, ForeignKey('links.id'))
      link = relation(Links)
  
      def __init__(self, title, link):  
          self.title = title
          self.link = link
  </code></pre>
  
  <p>However, I always get this error: </p>
  
  <pre><code>AttributeError: 'unicode' object has no attribute '_sa_instance_state'
  </code></pre>
  
  <p>What is going on? Is there a better way to code this?</p>