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
34945	annotate -> union -> values gives wrong values	Tom Carrick	nobody	"With the following code:

{{{
import uuid

from django.conf import settings
from django.contrib.auth import get_user_model
from django.db import models
from django.db.models.functions import Cast


class DocumentQuerySet(models.QuerySet):
    def for_user(self, user):
        return self.filter(things__user=user).union(
            self.filter(other_things__user=user)
        )


class Document(models.Model):
    name = models.CharField()
    id = models.UUIDField(default=uuid.uuid4, primary_key=True)

    objects = DocumentQuerySet().as_manager()


class Thing(models.Model):
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL, related_name=""things"", on_delete=models.CASCADE
    )
    document = models.ForeignKey(
        Document, related_name=""things"", on_delete=models.CASCADE
    )


class OtherThing(models.Model):
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL, related_name=""other_things"", on_delete=models.CASCADE
    )
    document = models.ForeignKey(
        Document, related_name=""other_things"", on_delete=models.CASCADE
    )


def broken():
    user = get_user_model().objects.first()
    return Document.objects.annotate(
        pk_str=Cast(""pk"", output_field=models.CharField())
    ).for_user(user).values_list(""pk_str"", flat=True)
}}}

Running `broken()`, I would expect to say the stringified UUIDs from the Document model. Instead I get the `name`s. It also happens when using `values()`. If not using either, it works just fine, and you can access `document.pk_str` and it works just fine. After playing with this, it seems to be because it's defined first in the model. If I move `id` to the top, it actually returns the UUIDs, without the cast being applied. The query (as far as I can tell from Django) looks fine:

{{{
(SELECT ""testapp_document"".""id"" AS ""col1"", ""testapp_document"".""name"" AS ""col2"", (""testapp_document"".""id"")::varchar AS ""pk_str"" FROM ""testapp_document"" INNER JOIN ""testapp_thing"" ON (""testapp_document"".""id"" = ""testapp_thing"".""document_id"") WHERE ""testapp_thing"".""user_id"" = 1) UNION (SELECT ""testapp_document"".""id"" AS ""col1"", ""testapp_document"".""name"" AS ""col2"", (""testapp_document"".""id"")::varchar AS ""pk_str"" FROM ""testapp_document"" INNER JOIN ""testapp_otherthing"" ON (""testapp_document"".""id"" = ""testapp_otherthing"".""document_id"") WHERE ""testapp_otherthing"".""user_id"" = 1)
}}}

And logged from Postgres also looks correct:
{{{
(SELECT ""testapp_document"".""name"" AS ""col1"", ""testapp_document"".""id"" AS ""col2"", (""testapp_document"".""id"")::varchar AS ""pk_str"" FROM ""testapp_document"" INNER JOIN ""testapp_thing"" ON (""testapp_document"".""id"" = ""testapp_thing"".""document_id"") WHERE ""testapp_thing"".""user_id"" = 1) UNION (SELECT ""testapp_document"".""name"" AS ""col1"", ""testapp_document"".""id"" AS ""col2"", (""testapp_document"".""id"")::varchar AS ""pk_str"" FROM ""testapp_document"" INNER JOIN ""testapp_otherthing"" ON (""testapp_document"".""id"" = ""testapp_otherthing"".""document_id"") WHERE ""testapp_otherthing"".""user_id"" = 1) LIMIT 21
}}}"	Bug	closed	Database layer (models, ORM)	4.2	Normal	duplicate			Unreviewed	0	0	0	0	0	0