Maps to explicit joins are in any case going to integrate poorly with
the joins created by SQLA's inheritance functionality. But in this
case, no imitation of SQLA's join is needed:
orm.mapper(Lab, inherits=Group,
polymorphic_identity=u"group_lab",
)
On Sep 6, 2008, at 1:24 PM, Jason Yamada-Hanff wrote:
> mport sqlalchemy as sa
> from sqlalchemy import types as t
> from sqlalchemy import orm
>
> engine = sa.create_engine('sqlite:///:memory:', echo=True)
> metadata = sa.MetaData()
>
> agents = sa.Table('agents', metadata,
> sa.Column('id', t.Integer,
> sa.Sequence('agents_id_seq', optional=True),
> primary_key=True),
> sa.Column('type', t.Unicode(50),
> sa.CheckConstraint("type IN ('agent', 'person', 'group',
> 'group_org', \
> 'group_lab', 'group_contactlist')"), nullable=False),
> sa.Column('notes', t.UnicodeText),
> )
>
> groups = sa.Table('groups', metadata,
> sa.Column('id', t.Integer, unique=True),
> sa.Column('short_name', t.Unicode(50)),
> sa.Column('name', t.Unicode(255), nullable=False),
> sa.Column('group_status', t.Unicode(50),
> sa.CheckConstraint("group_status IN ('active', 'not active',
> 'closed')"),
> default=u'active', nullable=False),
> sa.Column('description', t.UnicodeText),
> sa.PrimaryKeyConstraint('id'),
> sa.ForeignKeyConstraint(['id'], ['agents.id'],
> onupdate="CASCADE", ondelete="CASCADE")
> )
>
>
> class Agent(object):
> pass
>
> class Group(Agent):
> pass
>
> class Lab(Group):
> pass
>
>
> def map_agent_classes():
> orm.mapper(Agent, agents,
> polymorphic_on=agents.c.type,
> polymorphic_identity=u"agent",
> )
>
> orm.mapper(Group, groups,
> inherits=Agent,
> polymorphic_identity=u"group",
> )
>
> lab_select =
> agents.outerjoin(groups).select(agents.c.type==u'group_lab',\
> use_labels=True).alias('labs')
> orm.mapper(Lab, lab_select,
> inherits=Group,
> polymorphic_identity=u"group_lab",
> )
>
> map_agent_classes()
>
> metadata.create_all(engine)
> Session = orm.sessionmaker(bind=engine)
>
> sess = Session()
>
> lab = Lab()
> lab.name = u"Lab Name"
> lab.short_name = u"lab"
>
> sess.add(lab)
> sess.flush()
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