On Tuesday, May 28, 2019 at 9:10:19 AM UTC-4, Chris Wilson wrote:
>
> During initial load one can use a global session object,
>
You should not do that. Global sessions are widely considered an
anti-pattern.
I have discovered a limitation of TypeDecorators (custom column types):
> any one that uses the database (e.g. to load objects serialised in a custom
> way) has no way to know which database session to use.
>
While TypeDecorators are designed to offer control on how data is
encoded/decoded, they aren't really designed to do what you're attempting
(bootstrap an ORM relationship into a column, instead of a table). This is
the first time I've seen anyone try to do this, and I am a long time abuser
of SqlAlchemy myself.
Mike or Simon may have other suggestions, but my immediate thought is that
you can quickly accomplish what you're trying to do by just having a
TypeDecorator for `.cat_ids` serialize/deserialize a list of ids, and then
have a python @property for `def cats(self):` perform the sql needed to
turn `self.cat_ids` into `self.cats`. You'd be able to determine the
session for the actual object via `object_session`
@property
def cats(self):
if self._cats is None:
if self.cat_ids:
_session = object_session(self)
self._cats =
_session.query(Cats).filter(Cat.id.in_(self.cat_ids)).all()
return self._cats
--
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
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