SQLAlchemy, self-referential secondary table association

I'm trying to create a "Product" object in SQLAlchemy and so far I have gotten everything working accept the Product's "accessories". What I have is a Product with a list of field/value pairs (ie. Capacity : 12 L etc.), and integer ID and a catalog number. I would like to be able to associate certain "accessories" with a given product where these accessories are also products. Essentially I just want an association table that has product_id and accessory_id which both reference the ID in the Products table. This is what I have so far:

product_accessories=Table('product_accesssories',Base.metadata,\
                   Column('product_id',Integer,ForeignKey('product.product_id')),\
                   Column('accessory_id',Integer,ForeignKey('product.product_id')))

class Product(Base):
    __tablename__='product'
    id=Column('product_id',Integer,primary_key=True)
    catNo=Column('catalog_number',String(20))
    fields=relationship('ProductField')
    accessories=relationship('Product',secondary=product_accessories)

I get the error "Could not determine join condition between parent/child tables on relationship Product.accessories". I have tried fiddling around a bunch with this and haven't been able to get anywhere. I don't want开发者_C百科 to lose the unique reference to a product and I feel like there should be an easier way to do this other than wrapping accessories in another class.

Any help would be greatly appreciated!

import sqlalchemy as sa
from sqlalchemy import orm

products_table = sa.Table('products', metadata,
    sa.Column('id', sa.Integer(), primary_key=True),
    sa.Column('catalog_number', sa.String(20)),
)

accessories_table = sa.Table('product_accessories', metadata,
    sa.Column('product_id', sa.ForeignKey(products_table.c.id), primary_key=True),
    sa.Column('accessory_id', sa.ForeignKey(products_table.c.id), primary_key=True),
)

class Product(object):
    pass

class Accessory(object):
    pass

orm.mapper(Product, products_table, properties=dict(
    accessories=orm.relation(Accessory,
        primaryjoin=(products_table.c.id == accessories_table.c.product_id),
        secondaryjoin=(products_table.c.id == accessories_table.c.accessory_id),
    ),
))
orm.mapper(Accessory, accessories_table)