Add to SQLAlchemy Session in before_flush event?

[Roman Dubina]

Is there a proper way to add new object to Session while in before_flush event without infinite loop?

Example:

from sqlalchemy import event

@event.listens_for(SomeSessionOrFactory, 'before_flush')
def receive_before_flush(session, flush_context, instances):
    session.add(NEW_OBJECT)

I'm trying to make logging system for all models. Maybe there is a better way to do this? :)

[Mike Bayer]

no infinite loop is implicit in this activity. Feel free to provide an actual demonstration of your issue per the guidelines at http://stackoverflow.com/help/mcve. Here's a demo, thanks!

from sqlalchemy import Integer, Column, create_engine
from sqlalchemy.orm import Session
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)


e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)

s = Session(e)

from sqlalchemy import event


@event.listens_for(s, 'before_flush')
def receive_before_flush(session, flush_context, instances):
    session.add(A())

s.add_all([A(), A(), A()])
s.flush()

assert s.query(A).count() == 4

[Roman Dubina]

My mistake. Everything works great.