sqlalchemy.orm.exc.DetachedInstanceError depending on Pyramid webapp serving method? - orm

Question

This error in thrown only on production Apache2 server, and not at all when using pserve method to test the project locally :
sqlalchemy.orm.exc.DetachedInstanceError: Parent instance <My_Table at 0x7fc82076d2d0> is not bound to a Session; lazy load operation of attribute 'my_table_relationship' cannot proceed
Crashing code in template is:
<tal:x repeat="oMot_cn oMot_mcnii_cni.r_mcnii_cp.r_newphonets">
This kind of chained relationships pattern had been working well so far, I am just trying to load the whole query object at launching time of the Pyramid app, instead of loading a new one each time a request is handled by the view/controller...
It keeps crashing on production while it does not crash on pserve dev testing, so it's hard to debug.
Whole traceback on production server:
mod_wsgi (pid=15170): Exception occurred processing WSGI script '/var/local/env_py3/env_py3_2an/MyProject/myproject.wsgi'.
Traceback (most recent call last):
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/chameleon/template.py", line 170, in render
self._render(stream, econtext, rcontext)
File "tp_lesson_T_ex_mots_from_audio_765c6cd23ec517b3893410ce969cf2d9.py", line 584, in render
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/chameleon/py26.py", line 5, in lookup_attr
return getattr(obj, key)
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/sqlalchemy/orm/attributes.py", line 233, in __get__
return self.impl.get(instance_state(instance), dict_)
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/sqlalchemy/orm/attributes.py", line 579, in get
value = self.callable_(state, passive)
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/sqlalchemy/orm/strategies.py", line 479, in _load_for_state
(orm_util.state_str(state), self.key)
sqlalchemy.orm.exc.DetachedInstanceError: Parent instance <Caract_phonet at 0x7fc82076d2d0> is not bound to a Session; lazy load operation of attribute 'r_newphonets' cannot proceed
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/fanstatic/publisher.py", line 219, in __call__
return self.app(environ, start_response)
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/fanstatic/injector.py", line 64, in __call__
response = request.get_response(self.app)
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/webob/request.py", line 1296, in send
application, catch_exc_info=False)
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/webob/request.py", line 1260, in call_application
app_iter = application(self.environ, start_response)
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/pyramid/router.py", line 251, in __call__
response = self.invoke_subrequest(request, use_tweens=True)
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/pyramid/router.py", line 227, in invoke_subrequest
response = handle_request(request)
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/pyramid/tweens.py", line 21, in excview_tween
response = handler(request)
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/pyramid_tm-0.7-py3.2.egg/pyramid_tm/__init__.py", line 82, in tm_tween
reraise(*exc_info)
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/pyramid_tm-0.7-py3.2.egg/pyramid_tm/compat.py", line 13, in reraise
raise value
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/pyramid_tm-0.7-py3.2.egg/pyramid_tm/__init__.py", line 63, in tm_tween
response = handler(request)
File "/var/local/env_py3/env_py3_2an/lib/python3.2/site-packages/pyramid/router.py", line 161, in handle_request
response = view_callable(context, request)
Is there any missing PasteDeploy configuration to get it crashing the same way it does once it's pushed to production server ?