#36096: QuerySet.values() on a UNION query results in a broken query
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Reporter: Isaac Nygaard | Type:
| Uncategorized
Status: new | Component: Database
| layer (models, ORM)
Version: 5.0 | Severity: Normal
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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When calling `QuerySet.values()` on a union query, I get some internal
Django errors. For example:
{{{
qs = model.values(*grouping).annotate(**annotations)
// SAMPLE A: the following raises internal Django errors
t1 = qs.annotate(time_period=Value(1)).filter(filter_1)
t2 = qs.annotate(time_period=Value(2)).filter(filter_2)
qs = t1.union(t2).values(*values)
// SAMPLE B: the following works
t1 = qs.annotate(time_period=Value(1)).filter(filter_1).values(*values)
t2 = qs.annotate(time_period=Value(2)).filter(filter_2).values(*values)
qs = t1.union(t2)
}}}
Sample A fails because `qs.annotation_select` becomes different from
`t1.annotation_select` and `t2.annotation_select`. Django doesn't complain
until the query is run, and the database returns different columns (or
columns in a different order) than what it was expecting.
I would think Django should do one of the following:
1. have `qs.values()` update the selected annotations for its two child
combinator queries, t1/t2 (this is what I expected and why I wrote the
code that way)
2. disallow `values()` on union queries, e.g. by raising an informative
error
3. detect that `qs.annotation_select` columns do not match
`annotation_select` of the two child combinator queries and raise an
informative error
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Ticket URL: <https://code.djangoproject.com/ticket/36096>
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