#34254: Exists annotations can return non-boolean results (i.e. None) if used
with
an empty QuerySet.
-------------------------------------+-------------------------------------
Reporter: Keryn Knight | Owner:
| rajdesai24
Type: Bug | Status: assigned
Component: Database layer | Version: dev
(models, ORM) |
Severity: Normal | Resolution:
Keywords: Exists | Triage Stage: Accepted
EmptyQuerySet sqlite postgres |
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Keryn Knight):
Replying to [comment:1 Simon Charette]:
> I suspect the solution is as simple as setting
`Exists.empty_result_set_value = False` [...]
> [...]
> If you can confirm this addresses the problem you reported [...]
Confirming, it does seem to be as simple as that (a pleasant rarity in ORM
edge cases, I'm sure!) for the 2 backends I was testing (`postgres` and
`sqlite` -- I've notably not checked `mysql` or `oracle` etc):
{{{
In [3]:
A.objects.using("sqlite").annotate(should_be_bool=Exists(B.objects.none())).first().should_be_bool
Out[3]: False
In [4]:
A.objects.using("pg").annotate(should_be_bool=Exists(B.objects.none())).first().should_be_bool
Out[4]: False
}}}
The queries are still recorded as different, but I expect that's normal
coercion differences between sqlite & postgres:
{{{
In [6]: connections['sqlite'].queries
Out[6]:
[{'sql': 'SELECT "app_a"."id", 0 AS "should_be_bool" FROM "app_a" ORDER BY
"app_a"."id" ASC LIMIT 1',
'time': '0.001'}]
In [7]: connections['pg'].queries
Out[7]:
[{'sql': 'SELECT "app_a"."id", false AS "should_be_bool" FROM "app_a"
ORDER BY "app_a"."id" ASC LIMIT 1',
'time': '0.001'}]
}}}
---------------
WRT to fixing it, as rajdesai24 has expressed an interest in doing so,
I'll let them take the lead and get the contribution under their belt.
Replying to [comment:3 rajdesai24]:
> Hey Simon would love to submit a PR
--
Ticket URL: <https://code.djangoproject.com/ticket/34254#comment:4>
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