#25425: Enforce calling resolve_expression before as_sql on all expressions
-------------------------------------+-------------------------------------
Reporter: jarshwah | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by jarshwah):
Yes, but what about a resolvable nested within a non-resolvable. The docs
also (perhaps incorrectly) point out that resolve_expression is a place to
do validation
https://docs.djangoproject.com/en/1.8/ref/models/expressions/#django.db.models.Expression.resolve_expression
> Provides the chance to do any pre-processing or validation of the
expression before it’s added to the query. resolve_expression() must also
be called on any nested expressions. A copy() of self should be returned
with any necessary transformations.
If we want to support expressions as filters, then we're probably going to
have to support F() within a WhereNode():
{{{
Model.objects.filter(Greater(F('field'), 3)) -> WhereNode()
}}}
That WhereNode will have to be resolved at some point so that the nested
F() is also resolved. This was the major source of problems when
converting transforms into expressions:
https://github.com/django/django/blob/f2975c021d247bf8c6a5fc23988639c636da86f5/django/db/models/lookups.py#L76
I'm resolving the transform during the as_sql phase above which is wrong.
But it was way too hard trying to track down all of the places that
WhereNodes (and Lookups within the where node) were being rendered without
first being resolved. Which is the very reason for this ticket.
A WhereNode does not have to resolve to anything itself, but it has to
give nested expressions the chance to resolve.
--
Ticket URL: <https://code.djangoproject.com/ticket/25425#comment:2>
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