[Django] #31606: Cannot mix Exists expression with keyword arguments to When

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May 19, 2020, 2:18:37 AM5/19/20

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#31606: Cannot mix Exists expression with keyword arguments to When
------------------------------------------------+------------------------
Reporter: rheard | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: Uncategorized | Version: 3.0
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 1
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 1
UI/UX: 0 |
------------------------------------------------+------------------------
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"),
))
}}}

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.

--
Ticket URL: <https://code.djangoproject.com/ticket/31606>
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Django

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May 19, 2020, 2:20:06 AM5/19/20

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#31606: Cannot mix Exists expression with keyword arguments to When

-------------------------------------+-------------------------------------
Description changed by rheard:

Old description:

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.

--

--
Ticket URL: <https://code.djangoproject.com/ticket/31606#comment:1>

Django

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May 19, 2020, 2:31:07 AM5/19/20

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#31606: Cannot mix Exists expression with keyword arguments to When

-------------------------------------+-------------------------------------
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>

Django

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May 21, 2020, 8:13:00 PM5/21/20

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#31606: Cannot mix Exists expression with keyword arguments to When

Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 1 | UI/UX: 0

-------------------------------------+-------------------------------------
Changes (by Simon Charette):

* type: Cleanup/optimization => New feature
* version: 3.0 => master
* component: Uncategorized => Database layer (models, ORM)
* stage: Unreviewed => Accepted

--
Ticket URL: <https://code.djangoproject.com/ticket/31606#comment:3>

Django

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May 24, 2020, 11:59:39 PM5/24/20

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#31606: Cannot mix Exists expression with keyword arguments to When

Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 1 | UI/UX: 0

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

Comment (by felixxm):

[https://github.com/django/django/pull/12951 PR]

--
Ticket URL: <https://code.djangoproject.com/ticket/31606#comment:4>

Django

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May 25, 2020, 6:29:59 AM5/25/20

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#31606: Cannot mix Exists expression with keyword arguments to When

Has patch: 1 | Needs documentation: 1

Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 1 | UI/UX: 0

-------------------------------------+-------------------------------------
Changes (by felixxm):

* needs_docs: 0 => 1

--
Ticket URL: <https://code.djangoproject.com/ticket/31606#comment:5>

Django

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May 27, 2020, 1:31:47 AM5/27/20

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#31606: Cannot mix Exists expression with keyword arguments to When

-------------------------------------+-------------------------------------
Reporter: Ryan Heard | Owner: Ryan
| Heard
Type: New feature | Status: assigned

Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:

Keywords: | Triage Stage: Ready for
| checkin

Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 1 | UI/UX: 0

-------------------------------------+-------------------------------------
Changes (by felixxm):

* owner: nobody => Ryan Heard
* needs_docs: 1 => 0
* status: new => assigned
* stage: Accepted => Ready for checkin

--
Ticket URL: <https://code.djangoproject.com/ticket/31606#comment:6>

Django

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May 27, 2020, 1:56:51 AM5/27/20

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#31606: Cannot mix Exists expression with keyword arguments to When

-------------------------------------+-------------------------------------
Reporter: Ryan Heard | Owner: Ryan
| Heard

Type: New feature | Status: closed

Component: Database layer | Version: master
(models, ORM) |

Severity: Normal | Resolution: fixed

Keywords: | Triage Stage: Ready for
| checkin

Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 1 | UI/UX: 0

-------------------------------------+-------------------------------------
Changes (by Mariusz Felisiak <felisiak.mariusz@…>):

* status: assigned => closed
* resolution: => fixed

Comment:

In [changeset:"587b179d4115f2e4dbc425d1ae035be9eb22197b" 587b179d]:
{{{
#!CommitTicketReference repository=""
revision="587b179d4115f2e4dbc425d1ae035be9eb22197b"
Fixed #31606 -- Allowed using condition with lookups in When() expression.
}}}

--
Ticket URL: <https://code.djangoproject.com/ticket/31606#comment:7>

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