#10722: Changelist view does not use select_related() on a nullable foreign key
---------------------------+------------------------------------------------
Reporter: mrts | Owner: nobody
Status: new | Milestone:
Component: Uncategorized | Version: SVN
Keywords: | Stage: Unreviewed
Has_patch: 0 |
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Given the following `models.py`:
{{{
from django.db import models
class Base(models.Model):
name = models.CharField(max_length=10)
lots_of_text = models.TextField()
class Meta:
abstract = True
def __unicode__(self):
return self.name
class A(Base):
a_field = models.CharField(max_length=10)
class B(Base):
b_field = models.CharField(max_length=10)
class C(Base):
a = models.ForeignKey(A)
b = models.ForeignKey(B)
is_published = models.BooleanField()
}}}
and the following `admin.py`:
{{{
from django.contrib import admin
from improve_admin.models import A, B, C
class CAdmin(admin.ModelAdmin):
list_display = ('name', 'a', 'b', 'is_published')
admin.site.register(A)
admin.site.register(B)
admin.site.register(C, CAdmin)
}}}
`select_related()` is used as documented in
http://docs.djangoproject.com/en/dev/ref/contrib/admin/#list-select-
related , resulting in the following query:
{{{
SELECT
"improve_admin_c"."id", "improve_admin_c"."name",
"improve_admin_c"."lots_of_text", "improve_admin_c"."a_id",
"improve_admin_c"."b_id", "improve_admin_c"."is_published",
"improve_admin_a"."id", "improve_admin_a"."name",
"improve_admin_a"."lots_of_text", "improve_admin_a"."a_field",
"improve_admin_b"."id", "improve_admin_b"."name",
"improve_admin_b"."lots_of_text", "improve_admin_b"."b_field"
FROM
"improve_admin_c"
INNER JOIN "improve_admin_a" ON ("improve_admin_c"."a_id" =
"improve_admin_a"."id")
INNER JOIN "improve_admin_b" ON ("improve_admin_c"."b_id" =
"improve_admin_b"."id")
ORDER BY
"improve_admin_c"."id" DESC
}}}
----
Setting one foreign key field to be nullable:
{{{
# diff between the original and new models.py
class C(Base):
- a = models.ForeignKey(A)
+ a = models.ForeignKey(A, blank=True, null=True)
b = models.ForeignKey(B)
}}}
results in the following SQL:
{{{
SELECT
"improve_admin_c"."id", "improve_admin_c"."name",
"improve_admin_c"."lots_of_text", "improve_admin_c"."a_id",
"improve_admin_c"."b_id", "improve_admin_c"."is_published",
"improve_admin_b"."id", "improve_admin_b"."name",
"improve_admin_b"."lots_of_text", "improve_admin_b"."b_field"
FROM
"improve_admin_c"
INNER JOIN "improve_admin_b" ON ("improve_admin_c"."b_id" =
"improve_admin_b"."id")
ORDER BY
"improve_admin_c"."id" DESC
}}}
and additional `n` queries for each of the referred `a` fields:
{{{
SELECT
"improve_admin_a"."id", "improve_admin_a"."name",
"improve_admin_a"."lots_of_text", "improve_admin_a"."a_field"
FROM
"improve_admin_a"
WHERE
"improve_admin_a"."id" = 2
}}}
--
Ticket URL: <http://code.djangoproject.com/ticket/10722>
Django <http://code.djangoproject.com/>
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