title: Sqlalchemy: Many to Many relationship error
body: <p>Dear everyone, I am following the Many to many relationship described on <a href="http://www.sqlalchemy.org/docs/mappers.html#many-to-many" rel="nofollow noreferrer">http://www.sqlalchemy.org/docs/mappers.html#many-to-many</a></p>
  
  <pre><code>#This is actually a VIEW
  tb_mapping_uGroups_uProducts = Table( 'mapping_uGroups_uProducts', metadata,
      Column('upID', Integer, ForeignKey('uProductsInfo.upID')),
      Column('ugID', Integer, ForeignKey('uGroupsInfo.ugID'))
  )
  
  tb_uProducts = Table( 'uProductsInfo', metadata, 
      Column('upID', Integer, primary_key=True)
  )
  mapper( UnifiedProduct, tb_uProducts)
  
  tb_uGroupsInfo = Table( 'uGroupsInfo', metadata, 
      Column('ugID', Integer, primary_key=True)
  )
  mapper( UnifiedGroup, tb_uGroupsInfo, properties={
      'unifiedProducts': relation(UnifiedProduct, secondary=tb_mapping_uGroups_uProducts, backref="unifiedGroups")
  })
  </code></pre>
  
  <p>where the relationship between uProduct and uGroup are N:M.</p>
  
  <p>When I run the following </p>
  
  <pre><code>sess.query(UnifiedProduct).join(UnifiedGroup).distinct()[:10]
  </code></pre>
  
  <p>I am getting the error:</p>
  
  <pre><code>sqlalchemy.exc.ArgumentError: Can't find any foreign key relationships between 'uProductsInfo' and 'uGroupsInfo'
  </code></pre>
  
  <p>What am I doing wrong?</p>
  
  <p>EDIT: I am on MyISAM which doesn't support forigen keys</p>