Le 14/11/2012 06:19, Michael Bayer a écrit :
> On Nov 13, 2012, at 3:34 AM, tonthon wrote:
>
>> Hi,
>>
>> I'm using polymorphism for some of my models and I'm wondering how I
>> should use the with_polymorphic query method.
>>
>> Consider the following:
>> """
>> class A(Base):
>> type_ = Column(Integer, nullable=False)
>> arg = Column(String(20))
>> __mapper_args__ = {'polymorphic_on': type_, 'polymorphic_identity': 0}
>>
>> class B(A):
>> __mapper_args__ = {'polymorphic_identity': 1}
>>
>> class C(A):
>> __mapper_args__ = {'polymorphic_identity': 2}
>>
>> class D(A):
>> __mapper_args__ = {'polymorphic_identity': 3}
>> """
>>
>> When I query :
>>
>> """
>> session.query(A).with_polymorphic([B,C]).filter(A.arg == 'test')
>> """
>>
>> I get D elements in my result.
>> I've tried :
>>
>> """
>> session.query(A).with_polymorphic([B,C]).filter(or_(B.arg=='test',
>> C.arg=='test'))
>> """
>>
>> But it doesn't work neither.
>>
>> Could somebody explain me what I did wrong and how I should do ?
> with_polymorphic() is generally only useful with joined table inheritance
> (note this is single table inheritance), and is used to add those subclass
> tables to the Query so that you can filter() on their criterion, as well as
> to allow more columns to be pulled in via a single query rather than needing
> to invoke additional queries for subclass tables. It does not indicate a
> subset of subclasses to be included.
>
> If you want to load A's of type B, C, but not D, you'd need to do this
> manually via the discriminator - since B, C and D are all As you normally
> will get back all three as the rows determine.
>
> session.query(A).filter(A.type_.in(0, 1, 2))
>
Thanks for the answer, I had misunderstood the role of the
with_polymorphic method (In my app I'm using joined table inheritance).
Now it's far clearer.
Regards
Gaston
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