Maybe actually asking some questions would have helped getting
replies :-)
Is this not a bug? I may be wrong, but I would consider this a pretty
serious bug, as it does not raise an error, but silently returns the
wrong object, which could lead to serious data corruption...
If it is, should I just go ahead and open an entry in the tracker?
Thanks,
On Jul 2, 1:34 pm, Yves-Eric <[EMAIL PROTECTED]> wrote:
> Hi all,
>
> I have just spent most of a day tracking down a weird bug in an
> application I built on top of a legacy database, in which I use simple
> (non-polymorphic) multi-table inheritance. The problem arises when the
> parent and child tables share the same name for their primary key
> ("id" in my case), but with different values (each table has its own
> sequence).
>
> I illustrate the problem in the runnable script attached below, using
> a Person / Employee hierarchy. Most of the time, everything works fine
> (Employee alice1 has the right "alice" Person object). But when an
> Employee object is loaded (alice2), for which a Person object with the
> same id already exists in the session (bob was loaded, and bob's
> person.id happens to be the same as alice's employee.id), then the
> wrong parent object is loaded (Employee alice2 has the wrong Person
> object "bob").
>
> Here is a runnable script that reproduces this bug:
>
> ### BEGIN: multitable_inheritance_test.py ###
> from sqlalchemy import *
>
> db = create_engine('sqlite://', echo=False)
> __meta__ = BoundMetaData(db)
>
> person_table = Table("persons", __meta__,
> Column("id", Integer, primary_key=True),
> Column("name", String(80)),
> )
>
> employee_table = Table("employees", __meta__,
> Column("id", Integer, primary_key=True),
> Column("salary", Integer),
> Column("person_id", Integer, ForeignKey("persons.id")),
> )
>
> class Person(object):
> def __init__(self, name):
> self.name = name
>
> class Employee(Person): pass
>
> __meta__.create_all()
>
> person_mapper = mapper(Person, person_table)
> mapper(Employee, employee_table, inherits=person_mapper)
>
> person_insert = person_table.insert()
> person_insert.execute(id=1, name='alice')
> person_insert.execute(id=2, name='bob')
>
> employee_insert = employee_table.insert()
> employee_insert.execute(id=2, salary=250, person_id=1) # alice
> employee_insert.execute(id=3, salary=200, person_id=2) # bob
>
> session = create_session()
> query = session.query(Employee)
>
> alice1 = query.get(2)
> bob = query.get(3)
> alice2 = query.get(2)
>
> print 'alice1.name: %s' % alice1.name
> print 'alice2.name: %s' % alice2.name
>
> ### END ###
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