On Aug 17, 2010, at 5:05 PM, flzz wrote:
> Thanks this did the trick, I agree, an option in relationship to
> define how this behaves would be nice.
its a long term TODO.
>
> Cheers
> Etrik
>
> On Aug 17, 3:27 pm, Conor <conor.edward.da...@gmail.com> wrote:
>> 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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