[Django] #32898: get_or_create() with filter() has surprising behaviour

[Django]

#32898: get_or_create() with filter() has surprising behaviour
------------------------------------------+------------------------
Reporter: Jamie Cockburn | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 3.2
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
------------------------------------------+------------------------
This documentation:
https://docs.djangoproject.com/en/3.2/ref/models/querysets/#get-or-create

That doc says you can combine `filter()` with `get_or_create()`. Great!

But the resulting behaviour is somewhat surprising.

Given the following model:
{{{#!python
class A(models.Model):
a = models.CharField()
b = models.CharField()
}}}

I would expect that the following two lines would be fuctionally
equivalent:
{{{#!python
A.objects.get_or_create(a="something", b="another")
A.objects.filter(a="something").get_or_create(b="another")
}}}

If an instance `{"a": "something", "b": "another"}` already exists in the
database then they ''are'' equivalent.

If the instance does not exist, the `filter().get_or_create()` version
will create an instance `{"a": "", "b": "another"}`, throwing away the
kwargs passed to `filter()`.

By example:
{{{#!python
# create instance
o, c = A.objects.get_or_create(a='something', b="another")
print(o.a, o.b, c)

# find it with filter
o, c = A.objects.filter(a='something').get_or_create(b="another")
print(o.a, o.b, c)

# delete it again
A.objects.all().delete()

# create it with filter
o, c = A.objects.filter(a='something').get_or_create(b="another")
print(o.a, o.b, c)
}}}

Will output:
{{{
('something', 'another', True)
('something', 'another', False)
('', 'another', True)
}}}

This seems rather inconsistent, and should at least be flagged in the
docs.

--
Ticket URL: <https://code.djangoproject.com/ticket/32898>
Django <https://code.djangoproject.com/>
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[Django]

#32898: get_or_create() with filter() has surprising behaviour

--------------------------------+--------------------------------------

Reporter: Jamie Cockburn | Owner: nobody

Type: Uncategorized | Status: closed
Component: Uncategorized | Version: 3.2
Severity: Normal | Resolution: wontfix

Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0

--------------------------------+--------------------------------------
Changes (by Mariusz Felisiak):

* status: new => closed
* resolution: => wontfix

Comment:

Thanks for this report, however I don't see anything surprising or
confusing in the current behavior, implicit parameters passing would be
really unexpected. I also don't see much value in clarifying that
parameters are no passed implicitly. You can start a discussion on
DevelopersMailingList if you don't agree.

--
Ticket URL: <https://code.djangoproject.com/ticket/32898#comment:1>

[Django]

#32898: get_or_create() with filter() has surprising behaviour

-------------------------------------+-------------------------------------

Reporter: Jamie Cockburn | Owner: nobody

Type: New feature | Status: closed
Component: Database layer | Version: 3.2
(models, ORM) |
Severity: Normal | Resolution: wontfix

Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0

-------------------------------------+-------------------------------------
Changes (by Mariusz Felisiak):

* type: Uncategorized => New feature
* component: Uncategorized => Database layer (models, ORM)

--
Ticket URL: <https://code.djangoproject.com/ticket/32898#comment:2>