id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
16457	Deferred FKs make TestCase tests unreliable - no FK constraints checks at all!	Piotr Czachur	nobody	"Hi guys!

 * Database backends which have !DatabaseFeatures.can_defer_constraint_checks=True including Postgres psycopg2 create deferred FK during syncdb.
 * Deferred FK means that in case of ROLLBACK no constraing check is performed - illegal FK values are accepted.
 * !TestCase is using ROLLBACK to ""refresh"" database state - you can use illegal FKs in INSERT and UPDATE statemets - no error will be reported, which makes those tests unreliable.

I've noticed that deferred constraints are used by django.db.models.deletion.CASCADE(). Why no to use FK cascades if database supports it, and let user decide which cascades should be set?

Cheers!"	Bug	closed	Database layer (models, ORM)	1.3	Normal	duplicate			Unreviewed	0	0	0	0	0	0