#17000: sql/query.py add_q refactoring
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Reporter: akaariai | Owner: nobody
Type: | Status: new
Cleanup/optimization | Version: 1.3
Component: Database layer | Resolution:
(models, ORM) | Triage Stage: Design
Severity: Normal | decision needed
Keywords: | Needs documentation: 0
Has patch: 1 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
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Comment (by akaariai):
Actually, the correct approach might not be to defer the where/having
splitting to execution stage. Maybe it is to have an additional preprocess
stage before add_q instead.
The problem is that currently we are going into the q-objects blind. This
causes multiple issues: We might stumble upon aggregates (at which point
we must have the path information available to produce correctly negated
having tree), or we might stumble upon multi-joins (we use the except
`MultiJoin` in this case currently, and this isn't the cleanest of
approaches), or we might stumble upon filters that produce additional
filters (extra_filters, and the need to keep a fresh AND node constantly
at hand for this possibility, and the mutual recursion between
setup_joins() and add_filter()).
If we pre-processed the q-objects (travelled the lookup paths in the
q-objects, and checked what there is to expect) then the add_q
where/having logic would be much easier to refactor, the `MultiJoin` case
would be cleaner, and the extra_filters would be trivial to handle. The
benefits seem clear. Of course, without actual code many ideas seem
great... I definitely think this approach is worth investigating a lot
closer before proceeding further in this ticket. The start is to handle
the where/having split. The checking for extra_filters and MultiJoin needs
much larger changes.
--
Ticket URL: <https://code.djangoproject.com/ticket/17000#comment:5>
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