#32491: Updating a field based on a JSONField's sub-value adds extra quotes
[postgres]
-------------------------------------+-------------------------------------
Reporter: Baptiste Mispelon | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by Simon Charette):
* stage: Unreviewed => Accepted
Comment:
Bonjour Baptiste, always a pleasure to see you around :)
> Initially, I thought that adding an explicit Cast (using
update(name=Cast(F('data__name'), CharField()))) might solve the issue,
but the test still fails in the same way.
yeah that's expected since `::json::text` is pretty much the equivalent of
`json.dumps` (e.g. see #27257 for a similar problem)
> Adding to my confusion was the fact that this behavior doesn't appear
when using annotate: annotate(dataname=F('data__name')) correctly yields
django without the extra quotes.
Right this happens because `JSONField.from_db_value` attempts a
`json.loads` on the return value so `'"foo"' -> 'foo'`
> I'm not sure if this is really a bug or how fixable it is (I don't see
how Django could guess that it should use KeyTextTransform over
KeyTransform) but silently adding extra " seems pretty bad. Having
KeyTransform/KeyTextTransform documented could help, though I'm not sure
if I would have discovered their existence even if they were.
It could be done by having transforms used `for_save` have access to
`output_field` of the left hand side of the `UPDATE`/`INSERT` (e.g a
`CharField`) in this case and decide whether `->>` or `->` should be used
but that would be slightly backward incompatible.
An alternative could be to introduce an `__astext` lookup on `JSONField`
that would translate to the usage of `KeyTextTransform`. That would make
it explicit which SQL operator must be used and a similar approach could
be used for `__asint` and `__asfloat` to
[https://github.com/django/django/blob/64a0d1ef6e7a6739148996e9584bbb61fe3dcc60/django/db/models/fields/json.py#L462-L533
remove the lookups hacks for textual and numeric values] as right now it's
not possible to go things like `jsonfield__name__gt="Simon"`
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Ticket URL: <https://code.djangoproject.com/ticket/32491#comment:2>
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