ok, thanks for your aswers, I'll try it tonight.
2010/8/17 Michael Bayer <mike...@zzzcomputing.com>
>
> On Aug 16, 2010, at 4:20 AM, jean-philippe serafin wrote:
>
> AbstractA is AbstractB "base" class.........
> AbstractB is ClassA "base" class............
>
> Everything work fine in this case.
>
> I just want to set 'polymorphic_identity' on each inheritance level
> if I set by hand : update abstract_a set class_name = 'class_a' :
> AbstractA.query.first() give me back a ClassA object
>
>
>
> The reason you can't easily set "class_name" on the base is that you've
> named the attribute the same thing on both AbstractA and AbstractB. So
> AbstractB.class_name will never affect the basemost attribute on AbstractA.
> If you name them differently, your constructor can ensure they are set:
>
> def __init__(self, label):
>
> self.label = label
> self.class_name_a = self.class_name_b = self.__tablename__
>
> But what works better, merge them on AbstractB (still remove the
> unnecessary polymorphic_on from B, however), the value gets propagated to
> that of AbstractB:
>
> class AbstractA(Base):
>
> __tablename__ = "abstract_a"
>
> id = Column(Integer, primary_key=True)
> class_name = Column('class_name', String(50))
>
> __mapper_args__ = {
> 'polymorphic_on': class_name,
> }
>
> class AbstractB(AbstractA):
>
> __tablename__ = "abstract_b"
>
> id = Column(Integer, ForeignKey('abstract_a.id'),primary_key=True)
> class_name = column_property(Column('class_name', String(50)),
> AbstractA.__table__.c.class_name)
>
> __mapper_args__ = {
> 'polymorphic_identity': __tablename__,
> }
>
>
> Note however, it is not possible to load a ClassA object without querying
> at the very least "abstract_a". So the "class_name" column of "abstract_a"
> is always available with regular polymorphic querying. Its redundant and
> less normalized to have "class_name" on both tables with the same value
> (technically its not normalized in the first place to have a discriminator
> column at all, though it has a dramatically positive effect on our ability
> to locate subtypes without many outer joins). So there's no reason I can
> think of why you'd want class_name on B. But even if you did, there's
> still no reason to ever put polymorphic_on on a non-base table with the
> current implementation, and that should still be changed to emit a warning
> (#1880)- even here it would have alerted you to the issue.
>
>
>
>
>
> 2010/8/15 Michael Bayer <mike...@zzzcomputing.com>
>
>>
>> On Aug 15, 2010, at 6:52 AM, jean-philippe serafin wrote:
>>
>> > Hi,
>> >
>> > I've got a class mapping with two polymorphic inheritance :
>> >
>> > class AbstractA(Base):
>> >
>> > __tablename__ = "abstract_a"
>> >
>> > id = Column(Integer, primary_key=True)
>> > class_name = Column('class_name', String(50))
>> >
>> > __mapper_args__ = {
>> > 'polymorphic_on': class_name,
>> > }
>> > #some stuff here
>> >
>> > class AbstractB(AbstractA):
>> >
>> > __tablename__ = "abstract_b"
>> >
>> > id = Column(Integer, ForeignKey('abstract_a.id'),
>> > primary_key=True)
>> > class_name = Column('class_name', String(50))
>> >
>> > __mapper_args__ = {
>> > 'polymorphic_on': class_name,
>> > 'polymorphic_identity': __tablename__,
>> > }
>> > #some stuff here
>> >
>> > class ClassA(AbstractB):
>> >
>> > __tablename__ = "table_a"
>> > __mapper_args__ = {
>> > 'polymorphic_identity': __tablename__,
>> > }
>> >
>> > id = Column(Integer, ForeignKey('abstract_b.id'),
>> > primary_key=True)
>> > label = Column('label', String(50))
>> >
>> > def __init__(self, label):
>> > self.label = label
>> >
>> > I persist a ClassA object :
>> >
>> > object = ClassA('toto')
>> > db_session.add(object)
>> > db_session.commit()
>> >
>> > When I try to reload the object like this :
>> >
>> > reloaded_object = AbstractB.query.first()
>> >
>> > I get back a ClassA object (just fine)
>> >
>> > but when I try to reload like this :
>> >
>> > reloaded_object = AbstractA.query.first()
>> >
>> > I get back a AbstractA object because abstract_a.class_name has not
>> > been set to polymorphic_identity.
>> >
>> > Is this an issue or expected work?
>>
>> polymorphic_on only goes on the base class. SQLA should be changed to
>> raise an error on the setup you have above.
>>
>>
>> >
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