#30658: Unexpected result using union on two querysets with one annotating a
column
-------------------------------------+-------------------------------------
Reporter: Stefan | Owner: nobody
Wehrmeyer |
Type: Bug | Status: new
Component: Database | Version: 2.2
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 |
-------------------------------------+-------------------------------------
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.
--
Ticket URL: <https://code.djangoproject.com/ticket/30658>
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