# 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:PASSWORD@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'
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