#14030: Use F() objects in aggregates(), annotates() and values()
-------------------------------------+-------------------------------------
Reporter: delfick | Owner: smeatonj
Type: New feature | Status: assigned
Component: Database layer | Version: master
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: aggregate, annotate | Needs documentation: 0
Has patch: 1 | Patch needs improvement: 1
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
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Comment (by smeatonj):
The problem stems from the following block inside compiler.results_iter()
{{{
if has_annotation_select:
loaded_fields =
self.query.get_loaded_field_names().get(self.query.model, set()) or
self.query.select
annotation_start = len(self.query.extra_select) +
len(loaded_fields)
annotation_end = annotation_start +
len(self.query.annotation_select)
}}}
For certain queries, loaded_fields ends up being empty. The set of fields
appears to be fixed underneath the {{{ if resolve_columns }}} block, but
we still have a situation where annotation_start and end are effectively
wrong. Firstly, is the lack of a populated query.select already broken? I
don't think it is, because we branch off the truthiness in
resolve_columns. I think there is a bug here (expecting loaded_fields to
always be filled) that we've been lucky hasn't bitten us elsewhere.
What I'd like to do is completely remove these annotation_start/end
variables, and just add the output_type of the annotation to the set of
fields. Is there a particular reason that we aren't including the
output_type of the aggregate in the field list? It seems that backends
should have the opportunity to use resolve_columns to also inspect
aggregates. The only issue with that is I believe this is truly a bug (not
respecting loaded_fields), and should maybe be patched in a separate
ticket. Thoughts? I'll try and put together a patch on this branch to make
sure it's fixed, and we can extract it out if necessary.
--
Ticket URL: <https://code.djangoproject.com/ticket/14030#comment:47>
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