#27365: Fields suddenly not found.
-------------------------------------+-------------------------------------
Reporter: Brandon | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 1.9
(models, ORM) |
Severity: Normal | Resolution: needsinfo
Keywords: FieldDoesNotExist | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Brandon):
Further down the rabbit hole...
After figuring out that it was the occurance of {{{self.field_name ==
self.name}}} that was producing the problem I instrumented
{{{field_name}}} in {{{ForeignObjectRel}}} so that I could compare it to
{{{name}}}.
Here is the instrumentation I added to {{{ForeignObjectRel}}}
{{{
def _set_field_name(self,value):
name = getattr(self,'name',None)
field_name = value
if field_name and name and field_name == name:
import traceback
stacktrace = traceback.format_stack()
message = ''.join(["Bug#27365 - self.field_name ==
self.name\n"]+stacktrace)
warnings.warn(message, RuntimeWarning, stacklevel=2)
self._field_name=value
def _get_field_name(self):
name = getattr(self,'name',None)
field_name = getattr(self,'_field_name',None)
if field_name and name and field_name == name:
import traceback
stacktrace = traceback.format_stack()
message = ''.join(["Bug#27365 - self.field_name ==
self.name\n"]+stacktrace)
warnings.warn(message, RuntimeWarning, stacklevel=2)
return self._field_name
field_name = property(_get_field_name,_set_field_name)
}}}
This allowed me to see if *anything* in the system was setting
{{{self.field_name = self.name}}}, plus the exact trace to it in-situ.
As it turns out, it seems an old 3rd party application that adds metadata
to fields as attributes was reusing the attribute name {{{.field_name}}},
unaware that django was using it. I believe that the introduction of the
aggressive caching to relational objects that occurred between 1.7.x and
1.9.x allowed this errant use of {{{.field_name}}} to persist all the way
up until django attempted to reuse that object. Then when django reused
the object, {{{self.field_name}}} had been *sometimes* been incorrectly
set based on the caching + 3rd party app usage + life-time of the wsgi
process.
I have since deployed a monkey patch that alters the name of the metadata
field used by the 3rd party application so that it does not collide with
the relational object attribute {{{.field_name}}}.
I have not seen the error since.
--Brandon
--
Ticket URL: <https://code.djangoproject.com/ticket/27365#comment:12>
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