Opened 14 years ago

Closed 8 years ago

Last modified 8 years ago

#15250 closed Bug (fixed)

Cannot fill parent model instance in cache

Reported by: Vlastimil Zíma Owned by: Paulo
Component: Database layer (models, ORM) Version: 1.2
Severity: Normal Keywords:
Cc: Triage Stage: Accepted
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: yes
Easy pickings: no UI/UX: no

Description

Continue of #14371
I tried again in django trunk (tested also in 1.2.4)

I have following models (in SQLite3)

class Parent(models.Model):
    parent_int = models.IntegerField()

class Child(Parent):
    child_int = models.IntegerField()
In [1]: from django.db import connection

In [2]: from testmodule.models import Parent, Child

In [3]: Child.objects.create(parent_int = 1, child_int = 2)
Out[3]: <Child: Child object>

In [4]: Child.objects.get(parent_int = 1, child_int = 2).parent_ptr
Out[4]: <Parent: Parent object>

In [5]: connection.queries
Out[5]: 
[{'sql': u'INSERT INTO "testmodule_parent" ("parent_int") VALUES (1)',
  'time': '0.001'},
 {'sql': u'INSERT INTO "testmodule_child" ("parent_ptr_id", "child_int") VALUES (2, 2)',
  'time': '0.000'},
 {'sql': u'SELECT "testmodule_parent"."id", "testmodule_parent"."parent_int", "testmodule_child"."parent_ptr_id", "testmodule_child"."child_int" FROM "testmodule_child" INNER JOIN "testmodule_parent" ON ("testmodule_child"."parent_ptr_id" = "testmodule_parent"."id") WHERE ("testmodule_parent"."parent_int" = 1  AND "testmodule_child"."child_int" = 2 )',
  'time': '0.000'},
 {'sql': u'SELECT "testmodule_parent"."id", "testmodule_parent"."parent_int" FROM "testmodule_parent" WHERE "testmodule_parent"."id" = 2 ',
  'time': '0.000'}]

In [6]: Child.objects.select_related('parent').get(parent_int = 1, child_int = 2).parent_ptr
Out[6]: <Parent: Parent object>

In [7]: connection.queries
Out[7]: 
[{'sql': u'INSERT INTO "testmodule_parent" ("parent_int") VALUES (1)',
  'time': '0.001'},
 {'sql': u'INSERT INTO "testmodule_child" ("parent_ptr_id", "child_int") VALUES (2, 2)',
  'time': '0.000'},
 {'sql': u'SELECT "testmodule_parent"."id", "testmodule_parent"."parent_int", "testmodule_child"."parent_ptr_id", "testmodule_child"."child_int" FROM "testmodule_child" INNER JOIN "testmodule_parent" ON ("testmodule_child"."parent_ptr_id" = "testmodule_parent"."id") WHERE ("testmodule_parent"."parent_int" = 1  AND "testmodule_child"."child_int" = 2 )',
  'time': '0.000'},
 {'sql': u'SELECT "testmodule_parent"."id", "testmodule_parent"."parent_int" FROM "testmodule_parent" WHERE "testmodule_parent"."id" = 2 ',
  'time': '0.000'},
 {'sql': u'SELECT "testmodule_parent"."id", "testmodule_parent"."parent_int", "testmodule_child"."parent_ptr_id", "testmodule_child"."child_int" FROM "testmodule_child" INNER JOIN "testmodule_parent" ON ("testmodule_child"."parent_ptr_id" = "testmodule_parent"."id") WHERE ("testmodule_parent"."parent_int" = 1  AND "testmodule_child"."child_int" = 2 )',
  'time': '0.000'},
 {'sql': u'SELECT "testmodule_parent"."id", "testmodule_parent"."parent_int" FROM "testmodule_parent" WHERE "testmodule_parent"."id" = 2 ',
  'time': '0.000'}]

You can see that query is correct for selecting parent, but it's instance is not created in cache as usual and that leads to another select.

Attachments (1)

fill_parent_model_instance_1.diff (4.1 KB ) - added by marekw2143 14 years ago.

Download all attachments as: .zip

Change History (15)

comment:1 by Russell Keith-Magee, 14 years ago

Triage Stage: UnreviewedAccepted

Ok - thanks for the extra debug information. Looks like there is something going wrong here. As I indicated on #14371, the select_related() isn't necessary, but you've clearly shown that the parent object isn't being prepopulated as I said, either.

As a matter of procedure -- this is the sort of situation where it would have been ok to reopen the old ticket. It's the same problem, but by providing more debugging information you can demonstrate that the assertion I made was wrong. If that's the case, its perfectly acceptable to reopen an old ticket.

comment:2 by marekw2143, 14 years ago

Owner: changed from nobody to marekw2143
Status: newassigned

by marekw2143, 14 years ago

comment:3 by marekw2143, 14 years ago

Has patch: set

comment:4 by Łukasz Rekucki, 14 years ago

Severity: Normal
Type: Bug

comment:5 by Julien Phalip, 14 years ago

Needs tests: set

comment:6 by Aymeric Augustin, 13 years ago

Easy pickings: unset

See #16043 for a similar bug that has a test case.

comment:7 by marekw2143, 13 years ago

Owner: marekw2143 removed
Status: assignednew
UI/UX: unset

comment:8 by Tim Graham, 9 years ago

I closed #26523 as a duplicate (but it should be confirmed when solving this ticket).

comment:9 by Paulo, 8 years ago

Owner: set to Paulo
Status: newassigned

comment:10 by Paulo, 8 years ago

Needs tests: unset

comment:11 by Tim Graham, 8 years ago

Patch needs improvement: set

PR with some comments for improvement.

comment:12 by Tim Graham <timograham@…>, 8 years ago

Resolution: fixed
Status: assignedclosed

In 38575b00:

Fixed #15250 -- Avoided extra query on some multi-table inheritance queries.

Thanks marekw2143 for the initial patch and carljm for support.

comment:13 by Tim Graham <timograham@…>, 8 years ago

In 3e9f769:

Refs #15250 -- Added docstring for ForwardOneToOneDescriptor.

comment:14 by Simon Charette <charette.s@…>, 8 years ago

In 0bbab97:

Refs #15250 -- Removed an obsolete comment regarding MTI cascade deletion.

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