#24462: Add a new QuerySet operation to use current results as a subquery
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Reporter: trosos | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: dev
(models, ORM) |
Severity: Normal | Resolution:
Keywords: distinct order_by | Triage Stage: Accepted
subquery |
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 Jameel Al-Aziz):
I believe we have a similar need, but for difference reasons.
We have a JSONB postgres column and want to `jsonb_array_elements`
followed by filtering. Because `jsonb_array_elements` expands into a set
of columns, you cannot apply a `where` clause filter on the function
column. A simple solution is to use `jsonb_array_elements` in a subquery
and then filter the resulting subquery.
Another use case for sub-querying is being able to apply filters on union
queries. Our actual use case involves both `jsonb_array_elements` and
`UNION`s.
A sample query that I'm trying to write with querysets (but so far have
been unable to) is:
{{{
select *
from (
select id, jsonb_array_elements(json_data->'some_array') as elem
from foo as foo1
union
select id, jsonb_array_elements(json_data->'other_array') as elem
from foo as foo2
) as foo_w_elems
where (elem->>'subfield')::int in (
select id
from bar
where expires_at >= CURRENT_TIMESTAMP
)
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/24462#comment:9>
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