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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