#34255: Annotation/group by with an expression on psycopg3
-------------------------------------+-------------------------------------
Reporter: Guillaume Andreu | Owner: nobody
Sabater |
Type: Bug | Status: new
Component: Database layer | Version: dev
(models, ORM) |
Severity: Release blocker | Resolution:
Keywords: orm postgres | Triage Stage: Accepted
psycopg3 annotation groupby |
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 Simon Charette):
> I would love to see this done for Django in general and not at the
individual backend level. That said it is probably to late for 4.1
Agreed that it would be nice to get but there's no way we can squeeze it
in for 4.2.
> If we cannot fix the issue at hand nicely I think we could fall back to
client side cursors and provide a setting (backend option) to switch back
to server side cursors so people can experiment with them. Btw from the
looks of it and issues we ran into developing psycopg3 support, this also
means that the postgresql backend is basically the only backend using
server side bindings or is it just stricter than every other backend?
I'm not sure what you mean here by server side cursors. Did you mean
server side bindings?
I'm not sure what's causing it to be stricter but if pyscopg>=3 allows for
psycopg2 style of parameter bindings we should default to it until we can
figure out an adequate solution here. If that doesn't work I can commit
time to solving this issue but I fear the solution won't be pretty.
Basically we'd have to adapt `SQLCompiler.get_group_by` to do the
following
1. Change its return signature so it's allowed to return members that
should be added to the `SELECT` clause
2. Adjust
[https://github.com/django/django/blob/648005dee62481acc1784e5c9625e90f0fd6aab4/django/db/models/sql/compiler.py#L172
its compile logic] so when a compiled expression is parametrized
(`len(params) >= 1`) and is not part of `selected_expr_indices` then it's
added to of the members that must be added to the `SELECT` and are
returned by the method.
3. Then adjust `.as_sql` to the `SELECT *original_select (SELECT
*original_select, *extra_group_by_select ... GROUP BY ...
*extra_group_by_select_indices)` when there are `extra_group_by_select`
The only interesting bit is that we might be able to reuse some logic that
was added to implement window function filtering.
That's a lot of work to support server side bindings and that's only for
the group by clause, there might be other cases lurking around.
--
Ticket URL: <https://code.djangoproject.com/ticket/34255#comment:10>
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