On Fri, Oct 27, 2017 at 11:57 AM, <char...@konversion.ca> wrote:
> My SQLAlchemy version is 1.1.14.
>
> I'm having difficulty understanding behaviours around a polymorphic
> hierarchy.
>
> I have an AbstractConcreteBase and two subclasses.
>
> The ACB declares some attributes shared by the two subclasses, and the
> subclasses have attributes of their own that are not shared(i.e. they are
> not part of the shared identity represented by the ACB).
>
> class MyBase(AbstractConcreteBase, Base, Mixin):
> shared_id = Column(Integer, default=Sequence("database_shared_id_seq",
> start=0, increment=1), primary_key=True)
>
> @declared_attr
> def name(self):
> return Column(String(100), nullable=False)
>
> @declared_attr
> def foreign_key(self):
> return Column(Integer, ForeignKey("MyOtherTable.id"))
>
> ...
>
>
> class Concrete1(MyBase):
> start = Column(Date)
> end = Column(Date)
>
>
> class Concrete2(MyBase):
>
> @property
> def start(self):
> return self.details.start
>
> @property
> def end(self):
> return self.details.end
>
> details = relationship("Concrete2Detail", uselist=False, viewonly=True)
>
>
> As you can see, "start" and "end" are not declared in the ACB and are
> implemented differently between the table. I don't want them to be shared by
> the subclasses.
>
> When I query one of the Concretes, the ACB mapper is updated with the
> "start" and "end" attributes, and then the Concretes are expected to
> implement the attributes on the mapper level(which is not the case for
> Concrete2).
This is a natural effect of using an "abstract" base. When you try
to query polymorphically across Concrete1 and Concrete2, you're asking
it to query for the Concrete1.start and end columns. However it
should not in any way be modifying the Concrete2 mapper itself. I'm
not sure without running it what "are expected to implement" means.
An error is raised?
>
> How can I prevent this from happening?
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
> description.
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--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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