#31606: Cannot mix Exists expression with keyword arguments to When
-------------------------------------+-------------------------------------
Reporter: rheard | Owner: nobody
Type: | Status: new
Cleanup/optimization |
Component: Uncategorized | Version: 3.0
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 1 | UI/UX: 0
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Description changed by rheard:
Old description:
> I don't seem to be able to provide an Exists expression to When alongside
> keyword arguments like you can with filter. For instance, consider:
>
> {{{
> class State(models.Model):
> pass
>
> class County(models.Model):
> name = CharField(max_length=50)
> state = ForeignKey(State, related_name='counties')
> }}}
>
> I can execute the following query just fine:
>
> {{{
> County.objects.filter(
> Exists(State.objects.filter(counties=OuterRef('pk'), name="Texas")),
> name="Dallas",
> )
> }}}
>
> But a similar query using When does not work:
>
> {{{
> >>> County.objects.annotate(
> status=Case(
> When(Exists(State.objects.filter(counties=OuterRef('pk'),
> name="Texas")), name="Dallas", then=Value("DALLAS COUNTY")),
> default=Value("ELSEWHERE"),
> ))
> TypeError: When() supports a Q object, a boolean expression, or lookups
> as a condition.
> }}}
>
> Instead the arguments must be wrapped in a Q object:
>
> {{{
> >>> County.objects.annotate(
> status=Case(
> When(Q(Exists(State.objects.filter(counties=OuterRef('pk'),
> name="Texas")), name="Dallas"), then=Value("DALLAS COUNTY")),
> default=Value("ELSEWHERE"),
> ))
> }}}
>
> This is inconvenient and inconsistent with how filter works, as shown.
>
> When's __init__ method can be modified to allow similar input as filter.
> [https://github.com/rheard/django/commit/978e796bb18414d995d515ab7923831149300977
> Code is in a branch in my repo], but as this is my first time
> contributing to Django, I want to make sure I open a ticket and get
> feedback first.
New description:
I don't seem to be able to provide an Exists expression to When alongside
keyword arguments like you can with filter. For instance, consider:
{{{
class State(models.Model):
pass
class County(models.Model):
name = CharField(max_length=50)
state = ForeignKey(State, related_name='counties')
}}}
I can execute the following query just fine:
{{{
County.objects.filter(
Exists(State.objects.filter(counties=OuterRef('pk'), name="Texas")),
name="Dallas",
)
}}}
But a similar query using When does not work:
{{{
>>> County.objects.annotate(
status=Case(
When(Exists(State.objects.filter(counties=OuterRef('pk'),
name="Texas")), name="Dallas", then=Value("DALLAS COUNTY")),
default=Value("ELSEWHERE"),
))
TypeError: When() supports a Q object, a boolean expression, or lookups as
a condition.
}}}
Instead the arguments must be wrapped in a Q object:
{{{
>>> County.objects.annotate(
status=Case(
When(Q(Exists(State.objects.filter(counties=OuterRef('pk'),
name="Texas")), name="Dallas"), then=Value("DALLAS COUNTY")),
default=Value("ELSEWHERE"),
))
}}}
This is inconvenient and inconsistent with how filter works, as shown.
When's __init__ method can be modified to allow similar input as filter.
[https://github.com/rheard/django/commit/978e796bb18414d995d515ab7923831149300977
Code is in a branch in my repo], but as this is my first time contributing
to Django, I want to make sure I open a ticket and get feedback first.
Also I wasn't sure how to classify this. I wasn't sure if it was a bug, as
I wasn't sure if it was designed this way.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/31606#comment:2>
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