id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
31750	Abstract model field should not be equal across models	Ryan Hiebert	Ryan Hiebert	"Consider the following models:

{{{#!python
class A(models.Model):
    class Meta:
        abstract = True
    myfield = IntegerField()

class B(A):
    pass

class C(A):
    pass
}}}

If I pull the fields of {{{B}}} and {{{C}}} into a shared {{{set}}}, one will be de-duplicated away, because they compare as equal. I found this surprising, though in practice using a list was sufficient for my need. The root of the issue is that they compare equal, as fields only consider {{{self.creation_counter}}} when comparing for equality.

{{{#!python
len({B._meta.get_field('myfield'), C._meta.get_field('myfield')}) == 1
B._meta.get_field('myfield') == C._meta.get_field('myfield')
}}}

We should adjust {{{__eq__}}} so that if the {{{field.model}}} is different, they will compare unequal. Similarly, it is probably wise to adjust {{{__hash__}}} and {{{__lt__}}} to match.

When adjusting {{{__lt__}}}, it may be wise to order first by {{{self.creation_counter}}} so that cases not affected by this equality collision won't be re-ordered. In my experimental branch, there was one test that broke if I ordered them by model first.


I brought this up on IRC django-dev to check my intuitions, and those conversing with me there seemed to agree that the current behavior is not intuitive."	Bug	closed	Database layer (models, ORM)	3.0	Normal	fixed		Ryan Hiebert	Accepted	1	0	0	0	0	0