On 08/17/2010 11:21 AM, flzz wrote:
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy import create_engine, Column, Integer, String,
> ForeignKey
> from sqlalchemy.orm import sessionmaker, relationship
> from sqlalchemy.orm.collections import attribute_mapped_collection
>
> engine=create_engine('sqlite://', echo=True)
> Base = declarative_base(engine)
>
> def monkey_repr():
> def __repr__(self):
> """Show attribute values in the repr()."""
> simple_props = ', '.join('%s=%r' % (attr, value)
> for attr, value in
> sorted(vars(self).items())
> if isinstance(value, (basestring,
> int)))
> return '<%s (%s)>' % (type(self).__name__, simple_props)
> return __repr__
>
> Base.__repr__ = monkey_repr()
>
> class Company(Base):
> __tablename__ = 'companies'
> id = Column(Integer, primary_key=True)
> people = relationship('Person', lazy='joined',
>
> collection_class=attribute_mapped_collection('name'))
>
> class Person(Base):
> __tablename__ = 'people'
> id = Column(Integer, primary_key=True)
> _company_id = Column(Integer, ForeignKey('companies.id'))
> name = Column(String)
> discriminator = Column('type', String(50))
> __mapper_args__ = {'polymorphic_on': discriminator}
>
> class Engineer(Person):
> __tablename__ = 'engineers'
> __mapper_args__ = {'polymorphic_identity': 'engineer'}
> name = Column(String)
> department = Column(String)
> id = Column(Integer, ForeignKey('people.id'), primary_key=True)
> primary_language = Column(String(50))
>
> class Accountant(Person):
> __tablename__ = 'accountants'
> __mapper_args__ = {'polymorphic_identity': 'accountant'}
> name = Column(String)
> bank = Column(String)
> id = Column(Integer, ForeignKey('people.id'), primary_key=True)
> primary_language = Column(String(50))
>
> Base.metadata.create_all()
>
> sess = sessionmaker()()
>
> company = Company()
>
> for p in [Engineer(name='far'),
> Person(name='nar'),
> Engineer(name='zar', department='rover'),
> Accountant(name='jak', bank='hsb')]:
> company.people.set(p)
>
> sess.add(company)
> sess.commit()
> sess.expunge_all()
>
> print "\n#\n# Query for the first company \n#\n"
> c = sess.query(Company).first()
> print c.people
> print "\n#\n# This will issue another query even though lazy='joined'
> \n#\n"
> print c.people['zar'].department
>
The easiest way is to add a "with_polymorphic" argument to
Person.__mapper_args__:
class Person(object):
[...]
__mapper_args__ = {'polymorphic_on': discriminator,
'with_polymorphic': '*'}
The downside is that this will always enable joinedloads on the subclass
tables when loaded via relationships. Seems like it would be nice to add
a "with_polymorphic" parameter to relationship().
-Conor
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