[Sqlalchemy-tickets] Issue #2983: Insert deleted object problem with after flush listeners (zzzeek/sqlalchemy)

[Konsta V. <iss...@bi...>]

New issue 2983: Insert deleted object problem with after flush listeners
https://bitbucket.org/zzzeek/sqlalchemy/issue/2983/insert-deleted-object-problem-with-after

Konsta Vesterinen:

My guess is this problem is related to: https://bitbucket.org/zzzeek/sqlalchemy/issue/2501/the-delete-before-insert-problem

Failing test case:
```
#!python

import sqlalchemy as sa


dns = 'sqlite:///:memory:'

engine = sa.create_engine(dns)
engine.echo = True
connection = engine.connect()
Base = sa.ext.declarative.declarative_base()


class ModelA(Base):
    __tablename__ = 'a'

    id = sa.Column(sa.Integer, autoincrement=True, primary_key=True)
    name = sa.Column(sa.Unicode(255), nullable=False)


class ModelB(Base):
    __tablename__ = 'b'

    id = sa.Column(sa.Integer, autoincrement=True, primary_key=True)
    name = sa.Column(sa.Unicode(255), nullable=False)

Base.metadata.create_all(connection)

Session = sa.orm.sessionmaker(bind=connection)
session = Session()


@sa.event.listens_for(sa.orm.session.Session, 'after_flush')
def after_flush(session, flush_context):
    for obj in session:
        if not isinstance(obj, ModelA):
            continue
        b = session.query(ModelB).get(obj.id)
        if not b:
            b = ModelB(id=obj.id, name=u'b')
            session.add(b)
        else:
            b.name = u'updated b!'

a = ModelA(name=u'A')
session.add(a)
session.flush()
session.delete(a)
session.flush()
session.add(ModelA(id=a.id, name=u'A'))
session.commit()
b = session.query(ModelB).first()
assert b.name == u'updated b!'
```

This also throws a warning (which I think it should not throw): SAWarning: Attribute history events accumulated on 1 previously clean instances within inner-flush event handlers have been reset, and will not result in database updates. Consider using set_committed_value() within inner-flush event handlers to avoid this warning.