#29731: Type conversion should be possible with OuterRef
-------------------------------------+-------------------------------------
Reporter: tienne-B | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 2.1
(models, ORM) |
Severity: Normal | Resolution: invalid
Keywords: postgresql, sql, | Triage Stage:
json, outerref | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Simon Charette):
* status: new => closed
* resolution: => invalid
Comment:
Hey tienne-B,
Unfortunately it's not possible for Django, nor PostgreSQL, to
automatically determine that `context__key` (`"context" -> 'key'`) is a
string by the untyped and dynamic nature of the `jsonb` type. From
Django's perspective `context__key` is a `JSONField` and from PostgreSQL
it is `jsonb`.
This is the case because it's not possible to determine whether `url_key`
should be converted to `jsonb` or `"context" -> 'key'` to `text` so it is
necessary to provide an explicit cast as PostgreSQL suggests. I'd say that
here both Django and PostgreSQL refuse the temptation to guess.
Unfortunately calling `str` on `OuterRef` won't work as the Django ORM
doesn't implement this kind of ''high level magic'' like ORM such as
Peewee provide. In these cases you'll have to rely on either a `Cast`
[https://docs.djangoproject.com/en/2.1/ref/models/database-functions/#cast
function] or `KeyTextTransform` annotations instead.
For example using `Cast`.
{{{#!python
subquery = SentMessageRecord.objects.annotate(
context_key=Cast('context__key', models.CharField()),
).filter(
tournament=self.tournament,
email=OuterRef('email'),
context_key=OuterRef('url_key'),
event=SentMessageRecord.EVENT_TYPE_URL,
)
}}}
Given this isn't a defect with Django I'd say this would qualify as a
usage question and would better be addressed through support channels.
Without deterring you from reporting legitimate bugs it's always better to
confirm whether or not an issue can be resolved on support channels before
escalating to this tracker which is used to track defect and feature
requests.
--
Ticket URL: <https://code.djangoproject.com/ticket/29731#comment:1>
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