after_insert mapper event: can't populate target.BACKREF.attr

sector119

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Nov 8, 2011, 4:34:24 PM11/8/11

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Hello.

Why comments_after_insert_listener return None for target.report - backref for TripReport.comments?

class TripReportComment(Base):

__tablename__ = 'trip_report_comments'

id = Column(Integer, primary_key=True)

content = Column(UnicodeText, nullable=False)

report_id = Column(Integer, ForeignKey('trip_reports.id'), nullable=False)

def comments_after_insert_listener(mapper, connection, target):

print target.report

event.listen(TripReportComment, 'after_insert', comments_after_insert_listener)

class TripReport(Base):

__tablename__ = 'trip_reports'

id = Column(Integer, primary_key=True)

...

comments = relationship('TripReportComment', backref='report', cascade='all, delete-orphan', order_by='TripReportComment.id')

Michael Bayer

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Nov 8, 2011, 5:33:36 PM11/8/11

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On Nov 8, 2011, at 1:34 PM, sector119 wrote:

Hello.

Why comments_after_insert_listener return None for target.report - backref for TripReport.comments?

when you do...what exactly? this is just a mapping, looks fine. Can you provide a fully working example please ?

class TripReportComment(Base):
__tablename__ = 'trip_report_comments'

id = Column(Integer, primary_key=True)
content = Column(UnicodeText, nullable=False)
report_id = Column(Integer, ForeignKey('trip_reports.id'), nullable=False)

def comments_after_insert_listener(mapper, connection, target):
print target.report

event.listen(TripReportComment, 'after_insert', comments_after_insert_listener)

class TripReport(Base):
__tablename__ = 'trip_reports'

id = Column(Integer, primary_key=True)
...
comments = relationship('TripReportComment', backref='report', cascade='all, delete-orphan', order_by='TripReportComment.id')

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sector119

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Nov 9, 2011, 3:23:48 AM11/9/11

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# test_event.py

from sqlalchemy import create_engine

from sqlalchemy.orm import sessionmaker

from sqlalchemy.ext.declarative import declarative_base

from sqlalchemy import Column, ForeignKey

from sqlalchemy import Integer, UnicodeText

from sqlalchemy import event

from sqlalchemy.orm import relationship

engine = create_engine('postgresql+psycopg2://USER:PASS...@127.0.0.1:5432/test', echo=True)

Session = sessionmaker()

Base = declarative_base()

Session.configure(bind=engine)

Base.metadata.bind = engine

class Comment(Base):

__tablename__ = 'comment'

id = Column(Integer, primary_key=True)

content = Column(UnicodeText, nullable=False)

report_id = Column(Integer, ForeignKey('report.id'), nullable=False)

def comment_after_insert_listener(mapper, connection, target):

target.report.comments_count += 1

event.listen(Comment, 'after_insert', comment_after_insert_listener)

class Report(Base):

__tablename__ = 'report'

id = Column(Integer, primary_key=True)

content = Column(UnicodeText, nullable=False)

comments_count = Column(Integer, server_default='0', nullable=False)

comments = relationship('Comment', backref='report', cascade='all, delete-orphan', order_by='Comment.id')

Base.metadata.create_all(engine)

session = Session()

report = Report(content=u'test report')

session.add(report)

session.flush()

session.commit()

comment = Comment(content=u'test comment', report_id=1)

session.add(comment)

session.flush()

session.commit()

% /home/eps/tourclub/bin/python test_event.py

2011-11-09 10:19:38,970 INFO sqlalchemy.engine.base.Engine select version()

2011-11-09 10:19:38,970 INFO sqlalchemy.engine.base.Engine {}

2011-11-09 10:19:38,972 INFO sqlalchemy.engine.base.Engine select current_schema()

2011-11-09 10:19:38,972 INFO sqlalchemy.engine.base.Engine {}

2011-11-09 10:19:38,974 INFO sqlalchemy.engine.base.Engine select relname from pg_class c join pg_namespace n on n.oid=c.relnamespace where n.nspname=current_schema() and relname=%(name)s

2011-11-09 10:19:38,974 INFO sqlalchemy.engine.base.Engine {'name': u'report'}

2011-11-09 10:19:38,976 INFO sqlalchemy.engine.base.Engine select relname from pg_class c join pg_namespace n on n.oid=c.relnamespace where n.nspname=current_schema() and relname=%(name)s

2011-11-09 10:19:38,976 INFO sqlalchemy.engine.base.Engine {'name': u'comment'}

2011-11-09 10:19:38,978 INFO sqlalchemy.engine.base.Engine

CREATE TABLE report (

id SERIAL NOT NULL,

content TEXT NOT NULL,

comments_count INTEGER DEFAULT '0' NOT NULL,

PRIMARY KEY (id)

)

2011-11-09 10:19:38,978 INFO sqlalchemy.engine.base.Engine {}

2011-11-09 10:19:39,041 INFO sqlalchemy.engine.base.Engine COMMIT

2011-11-09 10:19:39,051 INFO sqlalchemy.engine.base.Engine

CREATE TABLE comment (

id SERIAL NOT NULL,

content TEXT NOT NULL,

report_id INTEGER NOT NULL,

PRIMARY KEY (id),

FOREIGN KEY(report_id) REFERENCES report (id)

)

2011-11-09 10:19:39,051 INFO sqlalchemy.engine.base.Engine {}

2011-11-09 10:19:39,134 INFO sqlalchemy.engine.base.Engine COMMIT

2011-11-09 10:19:39,145 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)

2011-11-09 10:19:39,146 INFO sqlalchemy.engine.base.Engine INSERT INTO report (content) VALUES (%(content)s) RETURNING report.id

2011-11-09 10:19:39,146 INFO sqlalchemy.engine.base.Engine {'content': u'test report'}

2011-11-09 10:19:39,147 INFO sqlalchemy.engine.base.Engine COMMIT

2011-11-09 10:19:39,151 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)

2011-11-09 10:19:39,152 INFO sqlalchemy.engine.base.Engine INSERT INTO comment (content, report_id) VALUES (%(content)s, %(report_id)s) RETURNING comment.id

2011-11-09 10:19:39,152 INFO sqlalchemy.engine.base.Engine {'content': u'test comment', 'report_id': 1}

2011-11-09 10:19:39,154 INFO sqlalchemy.engine.base.Engine ROLLBACK

Traceback (most recent call last):

File "test_event.py", line 54, in <module>

session.flush()

File "/home/eps/devel/tourclub/sqlalchemy/lib/sqlalchemy/orm/session.py", line 1547, in flush

self._flush(objects)

File "/home/eps/devel/tourclub/sqlalchemy/lib/sqlalchemy/orm/session.py", line 1616, in _flush

flush_context.execute()

File "/home/eps/devel/tourclub/sqlalchemy/lib/sqlalchemy/orm/unitofwork.py", line 328, in execute

rec.execute(self)

File "/home/eps/devel/tourclub/sqlalchemy/lib/sqlalchemy/orm/unitofwork.py", line 472, in execute

uow

File "/home/eps/devel/tourclub/sqlalchemy/lib/sqlalchemy/orm/mapper.py", line 2270, in _save_obj

mapper.dispatch.after_insert(mapper, connection, state)

File "/home/eps/devel/tourclub/sqlalchemy/lib/sqlalchemy/event.py", line 274, in __call__

fn(*args, **kw)

File "/home/eps/devel/tourclub/sqlalchemy/lib/sqlalchemy/orm/events.py", line 360, in wrap

wrapped_fn(*arg, **kw)

File "test_event.py", line 29, in comment_after_insert_listener

target.report.comments_count += 1

AttributeError: 'NoneType' object has no attribute 'comments_count'

sector119

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Nov 9, 2011, 7:16:09 AM11/9/11

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this works without any error, comment_after_insert_listener() prints that target.report.comments_count = 1, but this value isn't commited...

Can't get why prev testcase fails, this works, but target.report.comments_count value isn't saved :/