lazy="raise" on a many to one is problematic because a lot of many-to-one
operations involve pulling up the object from the identity map, and that's it.
since people are usually only trying to guard against SQL being emitted, use
the raise_on_sql option instead:
parent = relationship(Parent, lazy='raise_on_sql')
thanks for the perfect test case BTW makes this very easy for me
On Fri, Nov 22, 2019, at 6:12 AM, Marat Sharafutdinov wrote:
> from sqlalchemy import Column, ForeignKey, Integer, create_engine
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.orm import relationship, sessionmaker
>
> Base = declarative_base()
>
> class Parent(Base):
> __tablename__ = 'parents'
> id = Column(Integer, primary_key=True)
>
> class Child(Base):
> __tablename__ = 'children'
> id = Column(Integer, primary_key=True)
> parent_id = Column(Integer, ForeignKey(Parent.id))
> parent = relationship(Parent, lazy='raise', passive_deletes=True)
>
> engine = create_engine('sqlite:///:memory:', echo=True)
> Base.metadata.create_all(engine)
> Session = sessionmaker(bind=engine)
> session = Session()
>
> # Add
> parent = Parent()
> session.add(parent)
> session.flush()
> child = Child(parent_id=parent.id)
> session.add(child)
> session.commit()
>
> # Delete
> child = session.query(Child).first()
> session.delete(child)
> session.commit()
>
> Now I'm getting the following warning:
> /.venv/lib/python3.8/site-packages/sqlalchemy/orm/relationships.py:2021:
> SAWarning: On Child.parent, 'passive_deletes' is normally configured on
> one-to-many, one-to-one, many-to-many relationships only.
>
> If I change `parent` relationship as follows:
> parent = relationship(Parent, lazy='raise', backref=backref('children',
> passive_deletes=True))
> then I would get the following exception:
> sqlalchemy.exc.InvalidRequestError: 'Child.parent' is not available due to
> lazy='raise'
>
> How should it be made properly?
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
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> To post example code, please provide an MCVE: Minimal, Complete, and
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http://www.sqlalchemy.org/
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