#33403: Annotate results change when filtering *after* the annotate
-------------------------------------+-------------------------------------
Reporter: karyon | Owner: nobody
Type: | Status: new
Uncategorized |
Component: Database | Version: 4.0
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Publisher A has two books with each 100 pages.
{{{
Publisher.objects.annotate(Sum("books_pages"))
}}}
will give you 200 as the sum. However, adding a filter after the annotate
{{{
Publisher.objects.annotate(Sum("books_pages")).filter(books__in=Books.objects.all())
}}}
will give you 400. (apparently that's the correct sum 200 multiplied by
the number of books of that publisher)
I understand that joins in annotates can produce incorrect results, akin
to the one documented here:
[https://docs.djangoproject.com/en/4.0/topics/db/aggregation/#combining-
multiple-aggregations #combining-multiple-aggregations]. However, the docs
there say only "Combining multiple aggregations with annotate() will yield
the wrong results", and here I'm not combining multiple aggregations.
Furthermore, [https://docs.djangoproject.com/en/4.0/topics/db/aggregation
/#order-of-annotate-and-filter-clauses #order-of-annotate-and-filter-
clauses] says "When an annotate() clause is applied to a query, the
annotation is computed over the state of the query up to the point where
the annotation is requested.", which further made me believe this should
actually work.
--
Ticket URL: <https://code.djangoproject.com/ticket/33403>
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