Opened 17 years ago
Closed 16 years ago
#7173 closed (fixed)
Reverse of OneToOneField relationships are being cached improperly, returning wrong model class
Reported by: | George Vilches | Owned by: | nobody |
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Component: | Core (Other) | Version: | dev |
Severity: | Keywords: | 121, related_name, cache | |
Cc: | m.gajda@…, anossov@…, michal@… | Triage Stage: | Ready for checkin |
Has patch: | yes | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description
When following a reverse relationship, the cache where the objects pulled from the database are stored is not using the proper variable name for storing the reverse result. Two models both related to the original model will cause the relation to be overwritten on the second access, assuming that both models are related to the original model by the same name (and therefore are forced by the forward relationship to have a related_name attribute to distinguish them).
The solution, provided by Travis Terry (patch attached), is to cache by using the related_name instead of the field name.
Here's an example:
class Test4(models.Model): b = models.CharField(max_length=10) class Test5(models.Model): c = models.CharField(max_length=10) f2 = models.OneToOneField(Test4, related_name='first_link') class Test6(models.Model): d = models.CharField(max_length=10) f2 = models.OneToOneField(Test4, related_name='second_link') # This shows how to trigger the error. t4 = Test4.objects.create(b='Thing1') t5 = Test5.objects.create(c='obj1', f2=t4) t6 = Test6.objects.create(d='obj2', f2=t4) a = Test4.objects.get(pk=t4.id)
Here's what you get:
>>> print a.first_link Test5 object >>> print a.first_link.c obj1 >>> print a.second_link Test6 object >>> print a.second_link.d Traceback (most recent call last): ... AttributeError: 'Test5' object has no attribute 'd'
Here's what you should get:
>>> print a.first_link Test5 object >>> print a.first_link.c obj1 >>> print a.second_link Test6 object >>> print a.second_link.d obj2
Attachments (1)
Change History (8)
by , 17 years ago
Attachment: | related_cache_r7513.patch added |
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comment:1 by , 17 years ago
Component: | Uncategorized → Core framework |
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Has patch: | set |
comment:2 by , 17 years ago
Keywords: | 121 related_name cache added |
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comment:3 by , 17 years ago
Cc: | added |
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comment:4 by , 17 years ago
Cc: | added |
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comment:5 by , 17 years ago
Cc: | added |
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comment:6 by , 17 years ago
Triage Stage: | Unreviewed → Ready for checkin |
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Just traced the same problem and came up with the same solution.
More minimalistic example below (I believe it's easier to understand):
class A(Model): pass class B(Model): a = OneToOneField(A) class C(Model): a = OneToOneField(A) a = A() a.save() b = B(a=a) c = C(a=a) b.save() c.save() a = A.objects.get() a.b # <B: B object> a.c # <B: B object> -- WRONG!
I'm marking it as ready for checkin, unless we need regression tests.
comment:7 by , 16 years ago
Resolution: | → fixed |
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Status: | new → closed |
Patch from Travis Terry using related_name for the cache field name.