#10733: Invalid results when deferring fields in more than one related model
with
only()
---------------------------------------------------+------------------------
Reporter: mrts | Owner: nobody
Status: reopened | Milestone: 1.1
Component: Database layer (models, ORM) | Version: SVN
Resolution: | Keywords:
efficient-admin
Stage: Accepted | Has_patch: 1
Needs_docs: 0 | Needs_tests: 0
Needs_better_patch: 1 |
---------------------------------------------------+------------------------
Changes (by mrts):
* status: closed => reopened
* resolution: fixed =>
Comment:
Alas, given the above models, the following happens:
{{{
>>> from only_breakage.models import C
>>> from django.db import connection
>>> import copy
}}}
== Expected ==
All three tables joined:
{{{
>>> C.objects.all().only('name', 'a', 'b', 'a__name',
'b__name').select_related().query.as_sql()
('SELECT "only_breakage_c"."id", "only_breakage_c"."name",
"only_breakage_c"."a_id", "only_breakage_c"."b_id",
"only_breakage_a"."id", "only_breakage_a"."name",
"only_breakage_b"."id", "only_breakage_b"."name"
FROM "only_breakage_c"
INNER JOIN "only_breakage_a" ON ("only_breakage_c"."a_id" =
"only_breakage_a"."id")
INNER JOIN "only_breakage_b" ON ("only_breakage_c"."b_id" =
"only_breakage_b"."id")', ())
}}}
A single query fetches all what's needed:
{{{
>>> results = C.objects.all().only('name', 'a', 'b', 'a__name',
'b__name').select_related()
>>> connection.queries
[]
>>> results[0].a.name
u'a2'
>>> connection.queries
[{'sql': u'SELECT "only_breakage_c"."id", "only_breakage_c"."name",
"only_breakage_c"."a_id", "only_breakage_c"."b_id",
"only_breakage_a"."id", "only_breakage_a"."name",
"only_breakage_b"."id", "only_breakage_b"."name"
FROM "only_breakage_c"
INNER JOIN "only_breakage_a" ON ("only_breakage_c"."a_id" =
"only_breakage_a"."id")
INNER JOIN "only_breakage_b" ON ("only_breakage_c"."b_id" =
"only_breakage_b"."id")
LIMIT 1',
'time': '0.002'},
>>> queries = copy.deepcopy(connection.queries)
>>> results[0].b.name
u'b1'
>>> assert connection.queries == queries
}}}
== Actually got ==
Only two tables joined (the `A` table is discarded):
{{{
>>> C.objects.all().only('name', 'a', 'b', 'a__name',
'b__name').select_related().query.as_sql()
('SELECT "only_breakage_c"."id", "only_breakage_c"."name",
"only_breakage_c"."a_id", "only_breakage_c"."b_id",
"only_breakage_b"."id", "only_breakage_b"."name"
FROM "only_breakage_c"
INNER JOIN "only_breakage_b" ON ("only_breakage_c"."b_id" =
"only_breakage_b"."id")', ())
}}}
Three queries happen:
{{{
>>> results = C.objects.all().only('name', 'a', 'b', 'a__name',
'b__name').select_related()
>>> connection.queries
[]
>>> results[0].a.name
u'a2'
>>> connection.queries
[{'sql': u'SELECT "only_breakage_c"."id", "only_breakage_c"."name",
"only_breakage_c"."a_id", "only_breakage_c"."b_id",
"only_breakage_b"."id", "only_breakage_b"."name"
FROM "only_breakage_c" INNER JOIN "only_breakage_b" ON
("only_breakage_c"."b_id" = "only_breakage_b"."id") LIMIT 1',
'time': '0.002'},
{'sql': u'SELECT "only_breakage_a"."id", "only_breakage_a"."name",
"only_breakage_a"."lots_of_text", "only_breakage_a"."a_field" FROM
"only_breakage_a" WHERE "only_breakage_a"."id" = 2 ',
'time': '0.000'}]
>>> results[0].b.name
u'b1'
>>> connection.queries
[{'sql': u'SELECT "only_breakage_c"."id", "only_breakage_c"."name",
"only_breakage_c"."a_id", "only_breakage_c"."b_id",
"only_breakage_b"."id", "only_breakage_b"."name"
FROM "only_breakage_c" INNER JOIN "only_breakage_b" ON
("only_breakage_c"."b_id" = "only_breakage_b"."id") LIMIT 1',
'time': '0.002'},
{'sql': u'SELECT "only_breakage_a"."id", "only_breakage_a"."name",
"only_breakage_a"."lots_of_text", "only_breakage_a"."a_field" FROM
"only_breakage_a" WHERE "only_breakage_a"."id" = 2 ',
'time': '0.000'},
{'sql': u'SELECT "only_breakage_c"."id", "only_breakage_c"."name",
"only_breakage_c"."a_id", "only_breakage_c"."b_id",
"only_breakage_b"."id", "only_breakage_b"."name"
FROM "only_breakage_c" INNER JOIN "only_breakage_b" ON
("only_breakage_c"."b_id" = "only_breakage_b"."id") LIMIT 1',
'time': '0.000'}]
}}}
--
Ticket URL: <http://code.djangoproject.com/ticket/10733#comment:14>
Django <http://code.djangoproject.com/>
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