Need to add database features flag in some of the test cases

[rahul.priyadarshi@…]

Some of the Database backend doesn't allow to defer constraints check like DB2 which doesn't allow to defer constraint check within a transaction also

Following test cases requires to check can_defer_constraint_checks
i) test cases under admin_views.tests.AdminViewDeletedObjectsTest test class
ii) test cases under serializers_regress.tests.SerializerTests test class

Following test cases requires supports_forward_references flag check
i) serializers.SerializersTransactionTestBase.test_forward_refs
ii) fixtures_regress.TestFixtures.test_loaddata_works_when_fixture_has_forward_refs
iii) fixtures_regress.TestFixtures.test_loaddata_forward_refs_split_fixtures

[Michael Manfre]

Why does the patch use skipUnlessDBFeature in some places and skipUnless in others? Why not always use skipUnlessDBFeature?

[rahul.priyadarshi@…]

Yes, It would be good if always use skipUnlessDBFeature. In new attached patch(patch2.diff) I have made this modification.

[Tim Graham]

Couple of things I noticed:

• The MySQL backend has supports_forward_references=False (​blamed to 121d2e36), but after removing that (which changes it to True) the tests still pass (i.e. the existing test that has @skipUnlessDBFeature('supports_forward_references') is currently skipped on MySQL, but works fine). This issue is not necessarily related to this patch, except that additional tests that current pass on MySQL will be skipped. I'm not sure if supports_forward_references=False can be removed or if maybe it is only relevant for particular versions and/or storage engines in MySQL.

• MySQL + SQLite have can_defer_constraint_checks=False but admin_views.tests.AdminViewDeletedObjectsTest and serializers_regress.tests.SerializerTests current pass (the patch would cause them to be skipped).

[rahul.priyadarshi@…]

MySQL + SQLite can defer the constraint checking and can support forward reference until the end of the transaction. These test cases doing all the operation within a transaction only that's why these test case passes with MySQL+SQLite.

But it is not in case of dtatabse like DB2, which strictly follow constraint checking and can't defer it within a transaction also.

[Tim Graham <timograham@…>]

In 99f5ea9cc8f41724e07b88c6142d0092961ce5e0:

Fixed #22653 -- Added some database feature flags to tests.

Thanks Rahul Priyadarshi.

[Tim Graham <timograham@…>]

In 45e47f7b95aad98d91bb40e19dda14ae120980a4:

[1.7.x] Fixed #22653 -- Added some database feature flags to tests.

Thanks Rahul Priyadarshi.

Backport of 99f5ea9cc8 from master