many to many relation creattion failed

[shaverlee]

A typical many to many relation code like this (from Sqlalchemy's documents):

association_table = Table('association', Base.metadata,
Column('left_id', Integer, ForeignKey('left.id')),
Column('right_id', Integer, ForeignKey('right.id'))
)

class Parent(Base):
tablename = 'left'
id = Column(Integer, primary_key=True)
children = relationship("Child",
secondary=association_table)

class Child(Base):
tablename = 'right'
id = Column(Integer, primary_key=True)

after run "gearbox setup-app", the association_table didn't create, and the same code in Application's models worked correctly.
after I study the pluaggble's code, I found in sqla/models.py:

class SQLAModelsSupport(object):
def is_model(self, model):
return inspect.isclass(model) and hasattr(model, 'tablename')

so the subclass of Base has the attribute "tablename", but a instance of Table seems not.