Is there any way to get relationship joined loading to work from child back
up to the parent?
from sqlalchemy import create_engine, Column, Integer, String, ForeignKey
from sqlalchemy.orm import relationship, sessionmaker
from sqlalchemy.ext.declarative import declarative_base
engine = create_engine('sqlite:///:memory:')
Base = declarative_base()
class GrandParent(Base):
__tablename__ = 'grands'
id = Column(Integer, primary_key=True)
name = Column(String())
class Parent(Base):
__tablename__ = 'parents'
gp_id = Column(ForeignKey(GrandParent.id, ondelete='cascade'), nullable=
False)
gp = relationship(GrandParent, lazy='joined', innerjoin=True)
id = Column(Integer, primary_key=True)
name = Column(String())
class Child(Base):
__tablename__ = 'childs'
parent_id = Column(ForeignKey(Parent.id, ondelete='cascade'), nullable=
False)
parent = relationship(Parent, lazy='joined', innerjoin=True)
id = Column(Integer, primary_key=True)
name = Column(String())
Base.metadata.create_all(engine)
engine.echo = True
Session = sessionmaker(bind=engine)
session = Session()
gp = GrandParent(name='foo')
p = Parent(name='bar', gp=gp)
c = Child(name='baz', parent=p)
session.add(c)
session.commit()
# How many SQL statements? Why not 1 that would load Child, it's parent,
and it's grand parent?
assert c.parent.gp.id
As the last comment says, any way to get that last statement to issue one
join with all the inner joins to load the parent objects?
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