#29568: Avoid trying to UPDATE a parent model when its child just got INSERT
-------------------------------------+-------------------------------------
Reporter: François Dupayrat | Owner: nobody
Type: | Status: new
Cleanup/optimization |
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by François Dupayrat):
* has_patch: 0 => 1
Comment:
Pull request created: https://github.com/django/django/pull/10197
Tests showed a different behavior than the one listed in the ticket:
instead of doing UPDATE queries, SELECT queries were made in-between
INSERT INTO queries. Editing Parent, Child and GrandChild to add a Boolean
field revert to UPDATE queries.
In both cases, only INSERT INTO queries should be made anyway, so I don't
think it's necessary to add fields to Parent, Child or GrandChild.
Summary of queries:
- with existing I see 6 queries on GrandChild.objects.create()
{{{
INSERT INTO "model_inheritance_grandparent" ("first_name", "last_name",
"email", "place_id") VALUES ('', '', '', NULL)
SELECT (1) AS "a" FROM "model_inheritance_parent" WHERE
"model_inheritance_parent"."grandparent_ptr_id" = 1 LIMIT 1
INSERT INTO "model_inheritance_parent" ("grandparent_ptr_id") SELECT 1
SELECT (1) AS "a" FROM "model_inheritance_child" WHERE
"model_inheritance_child"."parent_ptr_id" = 1 LIMIT 1
INSERT INTO "model_inheritance_child" ("parent_ptr_id") SELECT 1
INSERT INTO "model_inheritance_grandchild" ("child_ptr_id") SELECT 1
}}}
- by adding a BooleanField with a default value to each of Parent, Child
and GrandChild, I still see 6 queries
{{{
INSERT INTO "model_inheritance_grandparent" ("first_name", "last_name",
"email", "place_id") VALUES ('', '', '', NULL)
UPDATE "model_inheritance_parent" SET "parent_field" = 1 WHERE
"model_inheritance_parent"."grandparent_ptr_id" = 1
INSERT INTO "model_inheritance_parent" ("grandparent_ptr_id",
"parent_field") SELECT 1, 1
UPDATE "model_inheritance_child" SET "child_field" = 1 WHERE
"model_inheritance_child"."parent_ptr_id" = 1
INSERT INTO "model_inheritance_child" ("parent_ptr_id", "child_field")
SELECT 1, 1
INSERT INTO "model_inheritance_grandchild" ("child_ptr_id",
"grand_child_field") SELECT 1, 1
}}}
- with patch I see 4 queries, both for modified and unmodified Models,
provided the new fields have default values.
{{{
INSERT INTO "model_inheritance_grandparent" ("first_name", "last_name",
"email", "place_id") VALUES ('', '', '', NULL)
INSERT INTO "model_inheritance_parent" ("grandparent_ptr_id") SELECT 1
INSERT INTO "model_inheritance_child" ("parent_ptr_id") SELECT 1
INSERT INTO "model_inheritance_grandchild" ("child_ptr_id") SELECT 1
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/29568#comment:6>
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