#17466: Model __eq__ does not compare correctly between normal objects and
deferred
objects
---------------------------------------------+--------------------
Reporter: Raphaël Hertzog <hertzog@…> | Owner: nobody
Type: Bug | Status: new
Component: Uncategorized | Version: 1.3
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
---------------------------------------------+--------------------
Enrico Zini <[email protected]> found a problem and reported it to the
Debian Bug Tracking System: http://bugs.debian.org/653177
I'll paste his report below:
----
I noticed that there is a problem with the default model object
{{{__eq__}}}
implementation when working with deferred objects.
The default implementation should be something like:
{{{
def __eq__(self, other):
return isinstance(other, self.__class__) and
self._get_pk_val() == other._get_pk_
val()
}}}
Now, given a simple model...
{{{
class Package(models.Model):
name = models.TextField(null=False, unique=True)
# Lots of other fields
}}}
...this code will show the problem:
{{{
# Get a normal object
p = Package.objects.get(name="debtags")
# Get a deferred object
dp = Package.objects.filter(name="debtags").only("name")[0]
print object.__repr__(p), hash(p)
print object.__repr__(dp), hash(dp)
# This assert succeeds
assert hash(p) == hash(dp)
# This assert fails
assert p == dp
}}}
Its output is:
{{{
<Package: debtags> 11
<Package_Deferred_ldesc_popcon_sdesc_source_version: debtags> 11
}}}
It looks like the isinstance bit of the default {{{__eq__}}} model is
failing
here.
This causes suprising behaviour:
{{{
allpkgs = set(Package.objects.all().only("name"))
# This assert fails
assert Package.objects.get(name="debtags") in allpkgs
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/17466>
Django <https://code.djangoproject.com/>
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