Hi,
I've been banging my head against this one for several days now, and
aside from a three year-old post here, I've come up empty.
I've got a python module that defines a set of Declarative models that
several other applications may use. What I'd like is some way to for the
individual applications to sub-class the existing Declarative objects,
without adding any new SQL functionality. Specifically, I'd just like to
add application-specific helper code to the objects. As an example.
some_model.py
---------------------------------------
[SQLA setup of Base class here]
class Alice(Base):
__tablename__ = 'alice'
id = Column(Integer, primary_key=True)
value = Column(String)
class Bob(Base):
__tablename__ = 'bob'
id = Column(Integer, primary_key=True)
subval = Column(String)
alice_id = Colum(Integer, ForeignKey('alice.id'))
alice = relationship('Alice', backref='bobs')
----------------------------------------
some_app.py
----------------------------------------
import some_model
class MyAlice(some_model.Alice):
def myfunc(self):
do_nothing_sql_related_here()
class MyBob(some_model.Bob):
def otherfunc(self):
again_something_unrelated()
-----------------------------------------
This actually works okay out of the box if I select on the subclasses:
DBSession.query(MyAlice).filter(MyAlice.id==5).first() -> MyAlice(...)
The problem, of course, is relations:
a = DBSession.query(MyAlice).filter(MyAlice.id=1).first()
a.bobs -> [Bob(...), Bob(...), Bob(...)]
instead of
a.bobs -> [MyBob(...), MyBob(...), MyBob(...)]
I suspect there's some way to tell the ORM to Do The Right Thing here, but
I have no idea what it might be. I'd like the particular applications to be
as unaware of the underlying table information as possible. I guess in
essence I'm trying to separate business logic from the DB logic as much as
possible. Maybe I'm heading down a dead-end... I'm open to better
suggestions.
Thanks,
Noah
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