This is semi-related to the latest post from Kent. I just noticed that I
have been abusing the "autoflush on begin" behavior (by the
_take_snapshot() method in orm/session.py) to create additional instances
within the after_flush Session Event. Here's some sample code to illustrate
that:
########
from sqlalchemy import event
from sqlalchemy.engine import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship, scoped_session, sessionmaker
from sqlalchemy.schema import Column, ForeignKey
from sqlalchemy.types import Integer, Text
Base = declarative_base()
engine = create_engine('postgresql://postgres@localhost/test')
Session = scoped_session(sessionmaker(
autoflush=False,
autocommit=False,
))
Session.configure(bind=engine)
class Ticket(Base):
__tablename__ = 'tickets'
id = Column(Integer, primary_key=True)
description = Column(Text, nullable=False)
class Notification(Base):
__tablename__ = 'notifications'
id = Column(Integer, primary_key=True)
ticket_id = Column(Integer, ForeignKey('tickets.id'), nullable=False)
ticket = relationship('Ticket', backref='notifications')
content = Column(Text, nullable=False)
def send_notification(session, flush_context):
for instance in session.new:
if isinstance(instance, Ticket):
Notification(
ticket=instance,
content='Ticket %d created' % instance.id,
)
# No flush or commit!
event.listen(Session, 'after_flush', send_notification)
Base.metadata.create_all(engine)
ticket = Ticket(description='test')
Session.add(ticket)
Session.commit()
query = Session.query(Notification).filter_by(
content='Ticket %d created' % ticket.id
)
assert query.count()
########
Although the code only does "Session.commit()" once, it actually executes 2
INSERT statements in 2 separate transactions. I am pretty sure this is not
an intended use case, right?
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