On Dec 21, 2012, at 7:14 AM, tonthon wrote:
> Hi,
>
> I've got a joined inheritance :
>
> class Task(Base):
> __tablename__ = 'task'
> id = Column(Integer, primary_key=True)
>
> class Invoice(Task):
> __tablename__ = 'invoice'
> id = Column(ForeignKey("task.id"))
>
> When I delete an invoice, the associated task is also deleted, that's ok.
>
> I've got a model TaskStatus related to the Task object and I'd like all
> related status to be deleted when I delete an invoice:
>
> class TaskStatus(Base):
> __tablename__ = 'task_status'
> id = Column(Integer, primary_key=True)
> task_id = Column(ForeignKey("task.id"))
> task = relationship("Task", backref=backref("statuses", cascade="all,
> delete-orphan"))
>
> How could I achieve that one ?
that mapping looks right to me, did you try it ?
an "ondelete='CASCADE'" can reduce the number of SELECT statements (see
http://docs.sqlalchemy.org/en/rel_0_8/orm/collections.html#using-passive-deletes)
but without it, "statuses" will load itself on flush and mark each of the
TaskStatus objects for deletion.
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Task(Base):
__tablename__ = 'task'
id = Column(Integer, primary_key=True)
type_ = Column(String)
__mapper_args__ = {'polymorphic_on': type_}
class Invoice(Task):
__tablename__ = 'invoice'
id = Column(ForeignKey("task.id"), primary_key=True)
__mapper_args__ = {'polymorphic_identity': 'invoice'}
class TaskStatus(Base):
__tablename__ = 'task_status'
id = Column(Integer, primary_key=True)
task_id = Column(ForeignKey("task.id"))
task = relationship("Task", backref=backref("statuses",
cascade="all, delete-orphan"))
e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
s = Session(e)
t1, t2, t3, t4 = TaskStatus(), TaskStatus(), TaskStatus(), TaskStatus()
i1 = Invoice(statuses=[t1, t2])
i2 = Invoice(statuses=[t3, t4])
s.add_all([i1, i2])
s.commit()
assert s.query(TaskStatus).count() == 4
s.delete(i1)
s.commit()
assert s.query(TaskStatus).count() == 2
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