#32965: Django related manager allways choose db_for_read router and fail
update/delete
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Reporter: Regressor | Owner: nobody
Type: Bug | Status: new
Component: Database | Version: 3.1
layer (models, ORM) | Keywords: related manager,
Severity: Normal | db_for_read, exception, db, router
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 have a large project running django 3.1.12. It is use aws aurora rds
cluster for database and we tried to take most of it. Wee need to use read
replicas to be able fast db overload response. So we made routers, started
multiple db config, fixed number read replica lag issues and finally got
error "cannot execute DELETE in a read-only transaction" in simple field
.delete()
So. Example: We have a model with a generic relation:
mentor_binds = GenericRelation('MentorBind',
object_id_field='parent_object_id',
content_type_field='parent_content_type')
And an exception when trying to clean binds:
instance.mentor_binds.all().delete()
The only workaround is to add .using('default') before .delete() /
.update()
I beelive this is a bug in GenericRelatedManager's _apply_rel_filters()
method. There is a string in it:
db = self._db or router.db_for_read(self.model, instance=self.instance)
But I can't say this is the only place with such problem, so I had to add
.using('default') before all .update() and .delete() - ~400 changes
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Ticket URL: <https://code.djangoproject.com/ticket/32965>
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