On Wed, Sep 23, 2009 at 5:34 PM, Conor <conor.edward.da...@gmail.com> wrote:
>
> You are missing a foreign key column in the "people" table that
> corresponds to your Person->Company relation. As a result, SQLAlchemy
> tries to use person.id as the foreign key column (because that column
> happens to be a foreign key to a base table of Company) and everything
> blows up.
>
Doh! I knew I was missing something basic.
So:
> * Add a foreign key column to Person that refers to companies.id.
> * Add a primaryjoin argument to your Persion.company relation, because
> SQLAlchemy will now see two potential ways to get from Person to
> Company (people.id -> bizentities.bizentity_id and people.company_id -
> > companies.id) and refuse to guess which path to take. Try
> "primaryjoin=lambda: Person.company_id == Company.__table__.c.id". I'm
> using Company.__table__.c.id instead of Company.id because Company.id
> maps to the "bizentities.bizentity_id" column and not the
> "companies.id" column.
>
> -Conor
>
>
Ah. I wouldn't have thought of the primaryjoin bit, so it's a good thing
you mentioned it. The traceback you get if you leave it out is a little
intimidating. :)
Thanks for this, Connor! Everything works now.
For the benefit of future searchers, here was the final model:
class BizEntity(Base):
__tablename__ = 'biz_entities'
id = Column('bizentity_id', Integer, primary_key=True)
type = Column('bizentity_type', String(30), nullable=False)
__mapper_args__ = {'polymorphic_on': type}
class Company(BizEntity):
__tablename__ = 'companies'
id = Column(Integer, ForeignKey('biz_entities.bizentity_id'),
primary_key=True)
name = Column('company_name', String(50))
__mapper_args__ = {'polymorphic_identity': 'company'}
def __init__(self, company_name):
self.name = company_name
def __repr__(self):
return "<Company('%s')>" % (self.name)
class Person(BizEntity):
__tablename__ = 'people'
id = Column('bizentity_id', Integer,
ForeignKey('biz_entities.bizentity_id'), primary_key=True)
first_name = Column('first_name', String(50))
middle_init = Column('middle_init', String(1))
last_name = Column('last_name', String(50))
company_id = Column(Integer, ForeignKey('companies.id'))
company = relation(Company,
primaryjoin=lambda: Person.company_id ==
Company.__table__.c.id,
backref=backref('employees', order_by=id))
__mapper_args__ = {'polymorphic_identity':'person'}
def __init__(self, first_name, middle_init, last_name):
self.first_name = first_name
self.middle_init = middle_init
self.last_name = last_name
def __repr__(self):
return "<Person('%s %s. %s')>" % (self.first_name, self.middle_init,
self.last_name)
Kevin Horn
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