SohpContext creates a Session, then loses it immediately. That's your
transactional context getting thrown away basically. You should have
a Session open for the lifespan of all ORM operations which includes
lazy loads. See
http://www.sqlalchemy.org/docs/04/session.html#unitofwork_contextual_lifespan
for some more ideas on this.
On Jun 12, 2008, at 1:06 PM, J. Cliff Dyer wrote:
>
> In the following code, I am using django templates to render data
> from a
> SQLAlchemy-mapped database. I subclass django.template.Context, so
> that
> I can pass it a unique ID, from which it determines what to pull from
> the DB. But when it comes time to render the template (that is:
> when I
> actually try to access data in the database), I get an
> UnboundExecutionError. If I instantiate the Context object
> directly, I
> don't have any problems. Any idea why this would be, and how I can
> get
> my class to work? I'd rather keep the lazy loading semantics
> intact, if
> possible.
>
> In the code below, render_1() has no problem, while render_2() raises
> the error. Below the code, I show the output I'm getting.
>
> #### CODE ####
> from django.conf import settings
> settings.configure()
>
> from django.template import Template, Context
>
> from sqlalchemy.orm.session import Session
> from cdla.orm import docsouth, docsouth_sohp
>
> class SohpContext(Context):
> def __init__(self, sohp_id):
> s = Session()
> q = s.query(docsouth_sohp.Interview)
> context_dict = {'interview':
> q.filter_by(sohp_id=sohp_id).one()}
> super(SohpContext, self).__init__(context_dict)
>
> def render_1(sohp_id):
> print "render_1"
> template = Template('''
> {% for p in interview.participants %}\
> * {{ p.participant.participant_firstname }}
> {% endfor %}''')
> s = Session()
> c = Context({'interview':
> s.query(docsouth_sohp.Interview).filter_by(sohp_id=sohp_id).one()})
> print template.render(c)
>
> def render_2(sohp_id):
> print "render_2"
> template = Template('''
> {% for p in interview.participants %}\
> * {{ p.participant.participant_firstname }}
> {% endfor %}''')
> c = SohpContext(sohp_id)
> print template.render(c)
>
> if __name__ == '__main__':
> render_1('A-0001')
> render_2('A-0001')
> #### END CODE ####
>
> #### RESULTS ####
> $ python error_reduce.py
> /net/docsouth/dev/lib/python/sqlalchemy/logging.py:62: FutureWarning:
> hex()/oct() of negative int will return a signed string in Python 2.4
> and up
> return "%s.%s.0x..%s" % (instance.__class__.__module__,
> render_1
>
> * Richard
> * Richard
> * Jack
> * Jack
>
> render_2
> Traceback (most recent call last):
> File "error_reduce.py", line 37, in ?
> render_2('A-0001')
> File "error_reduce.py", line 33, in render_2
> print template.render(c)
> File "/usr/lib/python2.3/site-packages/django/template/__init__.py",
> line 168, in render
> return self.nodelist.render(context)
> File "/usr/lib/python2.3/site-packages/django/template/__init__.py",
> line 705, in render
> bits.append(self.render_node(node, context))
> File "/usr/lib/python2.3/site-packages/django/template/__init__.py",
> line 718, in render_node
> return(node.render(context))
> File
> "/usr/lib/python2.3/site-packages/django/template/defaulttags.py",
> line
> 93, in render
> values = self.sequence.resolve(context, True)
> File "/usr/lib/python2.3/site-packages/django/template/__init__.py",
> line 563, in resolve
> obj = resolve_variable(self.var, context)
> File "/usr/lib/python2.3/site-packages/django/template/__init__.py",
> line 650, in resolve_variable
> current = getattr(current, bits[0])
> File "/net/docsouth/dev/lib/python/sqlalchemy/orm/attributes.py",
> line
> 44, in __get__
> return self.impl.get(instance._state)
> File "/net/docsouth/dev/lib/python/sqlalchemy/orm/attributes.py",
> line
> 279, in get
> value = callable_()
> File "/net/docsouth/dev/lib/python/sqlalchemy/orm/strategies.py",
> line
> 432, in __call__
> raise exceptions.UnboundExecutionError("Parent instance %s is not
> bound to a Session, and no contextual session is established; lazy
> load
> operation of attribute '%s' cannot proceed" % (instance.__class__,
> self.key))
> sqlalchemy.exceptions.UnboundExecutionError: Parent instance <class
> 'cdla.orm.docsouth_sohp.Interview'> is not bound to a Session, and no
> contextual session is established; lazy load operation of attribute
> 'participants' cannot proceed
> $
> #### END RESULTS ####
>
>
> >
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