Why don't you update the counter inside the add_post() operation? Updating the counter within the commit phase is broken and also trying to update the counter using a different session outside the current transaction is broken.
-aj
bismigalis wrote:
> I want in my Pyramid app to use SQLAchemy event 'after_insert', to
> update Topic model with number of posts belong to it.
>
> _views.py_
>
> def add_post(topic, request):
> post_form = PostForm(request.POST)
> if 'submit' in request.POST and post_form.validate():
> post = Post(body=post_form.body.data)
> post.user = request.user
> post.topic = topic
> DBSession.add(post)
> request.session.flash(_('Post was added'))
> transaction.commit()
> raise
> HTTPFound(location=request.route_url('topic',id=topic.id))
> return {'post_form':post_form}
>
> _models.py_
>
> class Topic(Base):
> __tablename__ = 'topics'
> id = Column(Integer, primary_key=True)
> ...
> post_count = Column(Integer, default=0)
> posts = relationship('Post',
> primaryjoin="Post.topic_id==Topic.id", backref='topic', lazy='dynamic')
>
>
> class Post(Base):
> __tablename__ = 'posts'
> id = Column(Integer, primary_key=True)
> ...
> topic_id = Column(Integer, ForeignKey('topics.id'))
>
>
> def post_inserted(mapper, conn, post):
> topic = post.topic
> topic.post_count = topic.posts.count()
>
> event.listen(Post, "after_insert", post_inserted)
>
> But I get exeption:
>
> Traceback (most recent call last):
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/waitress/channel.py",
> line 329, in service
> task.service()
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/waitress/task.py",
> line 173, in service
> self.execute()
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/waitress/task.py",
> line 380, in execute
> app_iter = self.channel.server.application(env, start_response)
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/pyramid/router.py",
> line 251, in __call__
> response = self.invoke_subrequest(request, use_tweens=True)
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/pyramid/router.py",
> line 227, in invoke_subrequest
> response = handle_request(request)
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/pyramid_tm/__init__.py",
> line 107, in tm_tween
> return response
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/transaction/_manager.py",
> line 116, in __exit__
> self.commit()
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/transaction/_manager.py",
> line 107, in commit
> return self.get().commit()
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/transaction/_transaction.py",
> line 354, in commit
> reraise(t, v, tb)
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/transaction/_transaction.py",
> line 345, in commit
> self._commitResources()
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/transaction/_transaction.py",
> line 493, in _commitResources
> reraise(t, v, tb)
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/transaction/_transaction.py",
> line 465, in _commitResources
> rm.tpc_begin(self)
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/zope/sqlalchemy/datamanager.py",
> line 86, in tpc_begin
> self.session.flush()
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/sqlalchemy/orm/session.py",
> line 1583, in flush
> self._flush(objects)
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/sqlalchemy/orm/session.py",
> line 1654, in _flush
> flush_context.execute()
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/sqlalchemy/orm/unitofwork.py",
> line 331, in execute
> rec.execute(self)
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/sqlalchemy/orm/unitofwork.py",
> line 475, in execute
> uow
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/sqlalchemy/orm/persistence.py",
> line 67, in save_obj
> states_to_insert, states_to_update)
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/sqlalchemy/orm/persistence.py",
> line 702, in _finalize_insert_update_commands
> mapper.dispatch.after_insert(mapper, connection, state)
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/sqlalchemy/event.py",
> line 291, in __call__
> fn(*args, **kw)
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/sqlalchemy/orm/events.py",
> line 360, in wrap
> wrapped_fn(*arg, **kw)
> File "/home/user/workspace/myforum/cube_forum/models.py", line
> 165, in post_saved
> topic.post_count = topic.posts.count()
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/sqlalchemy/orm/dynamic.py",
> line 249, in count
> sess = self.__session()
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/sqlalchemy/orm/dynamic.py",
> line 219, in __session
> sess.flush()
> File
> "/home/user/workspace/myforum/env/lib/python2.6/site-packages/sqlalchemy/orm/session.py",
> line 1577, in flush
> raise sa_exc.InvalidRequestError("Session is already flushing")
> InvalidRequestError: Session is already flushing
>
> I think if session already flushing, may be I need to start new
> db_session in event handler, how to do it right?
>
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