ok, everything is working as expected....
thanks, SQLAlchemy just rocks!
2010/8/17 jean-philippe serafin <serafi...@gmail.com>
> 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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>>
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