Hi all,
Before I post a bug ticket I'll post the question here. In sqlalchemy
0.58, I use single-table inheritance and a get-query (by primary key).
The get() queries for an Engineer with id 1, which does not exist
(since the row with id 1 represents a Manager). The query result seems
inconsistent to me: Sometimes you get None; and sometimes (when the
manager is already present in the session) you get the manager
instance.
Is this intended behavior or a bug? Test case below...
Cheers and thanks,
Martin
--------------------------------
from sqlalchemy import *
from sqlalchemy.orm import mapper, sessionmaker
engine = create_engine('sqlite:///:memory:', echo=True)
metadata = MetaData()
employees_table = Table('employees', metadata,
Column('employee_id', Integer, primary_key=True),
Column('name', String(50)),
Column('manager_data', String(50)),
Column('engineer_info', String(50)),
Column('type', String(20), nullable=False)
)
class Employee(object):
def __init__(self, name):
self.name = name
class Manager(Employee):
def __init__(self, name, manager_data):
self.name = name
self.manager_data = manager_data
class Engineer(Employee):
def __init__(self, name, engineer_info):
self.name = name
self.engineer_info = engineer_info
employee_mapper = mapper(Employee, employees_table, \
polymorphic_on=employees_table.c.type,
polymorphic_identity='employee')
manager_mapper = mapper(Manager, inherits=employee_mapper,
polymorphic_identity='manager')
engineer_mapper = mapper(Engineer, inherits=employee_mapper,
polymorphic_identity='engineer')
metadata.drop_all(engine)
metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()
session.add(Manager("Steve Jobs", "Apple CEO"))
session.commit()
session.add(Engineer("Steve Wozniak", "Apple engineer"))
session.commit()
# Need a new session in order to demonstrate
session = Session()
assert session.query(Engineer).get(1) is None # Works
assert isinstance(session.query(Manager).get(1), Manager)
assert session.query(Engineer).get(1) is None # Still works
manager = session.query(Manager).get(1)
assert session.query(Engineer).get(1) is None # fails!... is a Manager-
instance
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