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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