*Added support for Database Level Cascades* *PR link *: https://github.com/django/django/pull/16851
*Ref discussion : * https://groups.google.com/g/django-developers/c/Sxj7eS7-8SQ/m/jaM1rPbZEQAJ *Approach :* The on_delete argument for ForeignKey class now supports an extra option DB_CASCADE this will behave like DO_NOTHING in Django, but leverage the Database level cascading options supported by SQL. A new optional ar gument named on_delete_db is also passed to the ForeignKey. This will specify the type of database level cascading we are looking for if the on_delete is set to DB_CASCADE. Supported values of the on_delete_db argument can be the following: ON_DELETE_DB_CHOICES.DO_NOTHING_DB : Does nothing, used as default value. ON_DELETE_DB_CHOICES.CASCADE_DB : Deletes the child on parent deletion. ON_DELETE_DB_CHOICES.RESTRICT_DB : Prevent the deletion if child exists. ON_DELETE_DB_CHOICES.SET_NULL_DB : Set the value to null in child table. This will modify the SQL query during foreignkey generation. *Checks performed :* 1. on_delete = DB_CASCADE and the model containing the field has a non abstract parent model. As inherited the model contains a parent_ptr with in-python cascading options,(OneToOneField with on_delete=models.CASCADE) both cannot be used together. *Code :* https://github.com/django/django/blob/04df10e20853c8e549deddf46fac8c289e265225/django/db/models/fields/related.py#L1041 *Related testcase :* https://github.com/django/django/blob/04df10e20853c8e549deddf46fac8c289e265225/tests/db_cascade_checks/tests.py#L93 2. on_delete = DB_CASCADE and the model containing generic foreign keys or generic relation. In that case we prevent using DB_CASCADE too. *Code :* https://github.com/django/django/blob/04df10e20853c8e549deddf46fac8c289e265225/django/db/models/fields/related.py#L1060 *Related testcase :* https://github.com/django/django/blob/04df10e20853c8e549deddf46fac8c289e265225/tests/db_cascade_checks/tests.py#L144 3. Both on_delete and on_delete_db are specified. In order to specify the value of on_delete_db, on_delete must be set to DB_CASCADE. *Code :* https://github.com/django/django/blob/04df10e20853c8e549deddf46fac8c289e265225/django/db/models/fields/related.py#L1137 *Related testcase :* https://github.com/django/django/blob/04df10e20853c8e549deddf46fac8c289e265225/tests/db_cascade_checks/tests.py#L11 4. on_delete_db is set to SET_NULL_DB but the field is not nullable. *Code :* https://github.com/django/django/blob/04df10e20853c8e549deddf46fac8c289e265225/django/db/models/fields/related.py#L1150 *Related testcase :* https://github.com/django/django/blob/04df10e20853c8e549deddf46fac8c289e265225/tests/db_cascade_checks/tests.py#L66 5. Restricting the use of normal cascading if the foreignkey parent uses DB_CASCADING as this will generate untracable integrity errors. *Code :* 1. https://github.com/django/django/blob/04df10e20853c8e549deddf46fac8c289e265225/django/db/models/fields/related.py#L1104 2. https://github.com/django/django/blob/04df10e20853c8e549deddf46fac8c289e265225/django/db/models/fields/related.py#L1162 *Related testcase :* https://github.com/django/django/blob/04df10e20853c8e549deddf46fac8c289e265225/tests/db_cascade_checks/tests.py#L33 -- You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-developers+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/2b406f18-fbf1-4487-813b-582edf211971n%40googlegroups.com.
