#23270: select_related on fields pointing to subclasses does not work when using
defer
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Reporter: islavov | Owner: nobody
Type: Uncategorized | Status: new
Component: Database layer (models, ORM) | Version: 1.7-rc-2
Severity: Normal | Keywords: select_related
Triage Stage: Unreviewed | defer
Easy pickings: 0 | Has patch: 0
| UI/UX: 0
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I have the following models
{{{
#!python
from django.db import models
class Base(models.Model):
text = models.TextField()
class SubClassA(Base):
name = models.CharField(max_length=32)
}}}
In shell
{{{
#!python
In [3]: from defertest.models import SubClassA, Base
# Select related + defer
In [4]: c=Base.objects.select_related("subclassa").defer("text")[0]
(0.001) SELECT "defertest_base"."id", "defertest_subclassa"."base_ptr_id",
"defertest_subclassa"."name" FROM "defertest_base" LEFT OUTER JOIN
"defertest_subclassa" ON ("defertest_base"."id" =
"defertest_subclassa"."base_ptr_id") LIMIT 1; args=()
# We get an extra query when accessing the subclass
In [5]: c.subclassa
(0.000) SELECT "defertest_base"."id", "defertest_base"."text",
"defertest_subclassa"."base_ptr_id", "defertest_subclassa"."name" FROM
"defertest_subclassa" INNER JOIN "defertest_base" ON
("defertest_subclassa"."base_ptr_id" = "defertest_base"."id") WHERE
"defertest_subclassa"."base_ptr_id" = 1 ; args=(1,)
Out[5]: <SubClassA: SubClassA object>
# If no deferred fields
In [6]: c=Base.objects.select_related("subclassa")[0]
(0.000) SELECT "defertest_base"."id", "defertest_base"."text",
"defertest_subclassa"."base_ptr_id", "defertest_subclassa"."name" FROM
"defertest_base" LEFT OUTER JOIN "defertest_subclassa" ON
("defertest_base"."id" = "defertest_subclassa"."base_ptr_id") LIMIT 1;
args=()
# select related works fine ( no extra query )
In [7]: c.subclassa
Out[7]: <SubClassA: SubClassA object>
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/23270>
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