Created
September 26, 2018 15:35
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SQLAlchemy issue with joinedload and correlate_except on a column_property
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from sqlalchemy import create_engine, select, and_, func | |
from sqlalchemy.ext.declarative import declarative_base | |
from sqlalchemy import Boolean, Column, Integer, String, ForeignKey | |
from sqlalchemy.orm import sessionmaker, column_property, relationship, joinedload, deferred, undefer, load_only | |
engine = create_engine('sqlite:///:memory:', echo=True) | |
Session = sessionmaker(bind=engine) | |
session = Session() | |
Base = declarative_base() | |
class User(Base): | |
__tablename__ = 'users' | |
id = Column(Integer, primary_key=True) | |
name = Column(String) | |
fullname = Column(String) | |
password = Column(String) | |
group_id = Column(Integer, ForeignKey('groups.id')) | |
group = relationship('Group') | |
def __repr__(self): | |
return "<User(id=%d, name='%s', fullname='%s', password='%s')>" % ( | |
self.id, self.name, self.fullname, self.password) | |
class Worker(User): | |
__tablename__ = 'workers' | |
id = Column(Integer, ForeignKey('users.id', ondelete='CASCADE'), primary_key=True) | |
nino = Column(String) | |
employed = Column(Boolean) | |
group = relationship('WorkersGroup', backref='workers') | |
class Group(Base): | |
__tablename__ = 'groups' | |
id = Column(Integer, primary_key=True) | |
name = Column(String) | |
def __repr__(self): | |
return "<Group(id=%d, name='%s')>" % (self.id, self.name) | |
class WorkersGroup(Group): | |
__tablename__ = 'workers_groups' | |
id = Column(Integer, ForeignKey('groups.id', ondelete='CASCADE'), primary_key=True) | |
def __repr__(self): | |
return "<WorkersGroup(id=%d, name='%s', count='%r')>" % ( | |
self.id, self.name, self.employee_count) | |
WorkersGroup.employee_count = column_property( | |
select([func.count(Worker.id)]).where( | |
and_( | |
Worker.id == User.id, | |
Worker.group_id == WorkersGroup.id, | |
Worker.nino.isnot(None) | |
) | |
).correlate_except(Worker, User) | |
) | |
Base.metadata.create_all(engine) | |
workers = WorkersGroup(name='workers') | |
session.add(workers) | |
contractors = WorkersGroup(name='contractors') | |
session.add(contractors) | |
session.flush() | |
ed_user = User(name='ed', fullname='Ed Jones', password='edspassword') | |
session.add(ed_user) | |
ed1_user = Worker(name='ed1', fullname='Ed1 Jones', group_id=workers.id, nino='ABC123') | |
session.add(ed1_user) | |
ed2_user = Worker(name='ed2', fullname='Ed2 Jones', group_id=workers.id) | |
session.add(ed2_user) | |
ed3_user = Worker(name='ed3', fullname='Ed3 Jones', group_id=contractors.id, nino='CBA321') | |
session.add(ed3_user) | |
ed4_user = Worker(name='ed4', fullname='Ed4 Jones', group_id=contractors.id, nino='CBA321') | |
session.add(ed4_user) | |
ed5_user = Worker(name='ed5', fullname='Ed5 Jones', group_id=contractors.id, nino='CBA321') | |
session.add(ed5_user) | |
session.flush() | |
# Depending on which of the following blocks happen first, the result is either 1 or 3 | |
# Block 1 | |
w = session.query(Worker).filter(Worker.id == 4).one() | |
print(w) | |
print(w.group.employee_count) | |
# Block 2 | |
w = session.query(Worker).options(joinedload(Worker.group)).filter(Worker.id == 4).one() | |
print(w) | |
print(w.group.employee_count) |
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