#30382: force_insert not respected when saving parents
-------------------------------------+-------------------------------------
Reporter: Phill | Owner: nobody
Tornroth |
Type: Bug | Status: new
Component: Database | Version: 2.2
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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We're using non-abstract model inheritance (table per model class) and
issuing our own primary keys. When saving we pass force_insert=True to
prevent the extra UPDATE statement that precedes the INSERT. The
force_insert flag is respected on the child table but not on the parent.
So given:
{{{
class ParentModel(models.Model):
id = models.BigIntegerField(primary_key=True)
class ChildModel(ParentModel):
pass
ChildModel(id=1).save(force_insert=True)
}}}
We'll see queries:
1. UPDATE app_parentmodel (no rows affected)
2. INSERT app_parentmodel
3. INSERT app_childmodel
This is because Model.save_base doesn't pass force_insert along to
Model._save_parents, and onto Model._save_table. Doing so would prevent
the extra UPDATE and respect the spirit of the force_insert feature. This
is a change I've made locally and seems to work / is pretty
straightforward. I'm curious though if there's intent behind not carrying
the force_insert functionality through for parents. I couldn't find any
discussion on the topic.
For context about why this is particularly problematic in our case --
we're using MySQL w/ Innodb and Innodb will take out different exclusive
locks for the UPDATE and INSERT in question -- so if you're creating new
ChildModel instances in parallel you can get deadlocks when multiple
threads issue query #1 and then need a lock with insert intention in order
to get #2.
--
Ticket URL: <https://code.djangoproject.com/ticket/30382>
Django <https://code.djangoproject.com/>
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