SA deferred load possible bug / basic demo

sa_defer_simple.py

from sqlalchemy import (
    create_engine,
    inspect,
    Column,
    ForeignKey,
    Integer
)
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import (
    defer,
    joinedload,
    relationship,
    sessionmaker,
    subqueryload,
)

Base = declarative_base()

class Parent(Base):
    __tablename__ = 'parent'
    id = Column(Integer, primary_key=True)
    stuff = Column(Integer)
    children = relationship('Child', back_populates='parent')


class Child(Base):
    __tablename__ = 'child'
    id = Column(Integer, primary_key=True)
    parent_id = Column(Integer, ForeignKey('parent.id'))
    parent = relationship('Parent', back_populates='children')


def load(session):
    p = Parent()
    c = Child()
    p.children.append(c)
    session.add_all([p, c])


def run(session):
    result = session.query(Parent).options(
        defer(Parent.stuff),
        joinedload('children').subqueryload('parent').options(
            defer(Parent.stuff))
    ).one()
    
    insp = inspect(result)
    print('callables:', insp.callables)
    assert 'stuff' in insp.callables, 'deferred `Parent.stuff` should be available as a callable'


engine = create_engine('sqlite:///:memory:', echo=True)
Base.metadata.create_all(engine)

Session = sessionmaker(bind=engine)
session = Session()
load(session)
run(session)
session.close()


# # 1.3.23
# SELECT parent.id AS parent_id, child_1.id AS child_1_id, child_1.parent_id AS child_1_parent_id
# FROM parent
# LEFT OUTER JOIN child AS child_1 ON parent.id = child_1.parent_id
# 
# SELECT parent.id AS parent_id, child_1.parent_id AS child_1_parent_id
# FROM (SELECT parent.id AS parent_id FROM parent) AS anon_1
# JOIN child AS child_1 ON anon_1.parent_id = child_1.parent_id
# JOIN parent ON parent.id = child_1.parent_id
# 
# # 1.4.5
# SELECT parent.id AS parent_id, child_1.id AS child_1_id, child_1.parent_id AS child_1_parent_id 
# FROM parent
# LEFT OUTER JOIN child AS child_1 ON parent.id = child_1.parent_id
# 
# SELECT parent.id AS parent_id, parent.stuff AS parent_stuff, child_1.parent_id AS child_1_parent_id 
# FROM (SELECT parent.id AS parent_id FROM parent) AS anon_1
# JOIN child AS child_1 ON anon_1.parent_id = child_1.parent_id
# JOIN parent ON parent.id = child_1.parent_id