id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
30658	Unexpected result using union querysets with annotated columns.	Stefan Wehrmeyer	nobody	"I have two models:

{{{
class ModelA(models.Model):
    column_a = models.CharField(max_length=255, blank=True)
    column_b = models.CharField(max_length=255, blank=True)


class ModelB(models.Model):
    column_b = models.CharField(max_length=255, blank=True)

}}}

I want to query both at once using `union`, filling in a default value for `column_a` in `ModelB`:


{{{
from django.db.models import Value, CharField

ModelA.objects.create(
    column_a='a',
    column_b='b',
)
ModelB.objects.create(
    column_b='b',
)

columns = ('column_a', 'column_b')

a_qs = ModelA.objects.all().values(*columns)
b_qs = (
    ModelB.objects.all()
    .annotate(
        column_a=Value(""a"", output_field=CharField())
    )
    .values(*columns)
)
qs = a_qs.union(b_qs)
qs
}}}

This leads to the following unexpected output:

{{{
<QuerySet [{'column_a': 'a', 'column_b': 'b'}, {'column_a': 'b', 'column_b': 'a'}]>
}}}

Note that the second row in the result (coming from `b_qs`) has the values for the columns mixed up!

The SQL query is:
{{{
print(qs.query)
SELECT ""example_modela"".""column_a"", ""example_modela"".""column_b"" FROM ""example_modela"" UNION SELECT ""example_modelb"".""column_b"", a AS ""column_a"" FROM ""example_modelb""
}}}

I'm not sure if I'm using the ORM in a wrong way. I would consider my use case (=union+annotate) valid and would expect some kind of error if the ORM was not able to deal with it."	Bug	closed	Database layer (models, ORM)	dev	Normal	duplicate			Unreviewed	0	0	0	0	0	0