migration_test_data_persistence fails when running with parallelism > 1 and Postgres

[Raphael Gaschignard]

Steps to reproduce:

• Add the following file to tests, as test_postgres.py

import os

from test_sqlite import *  # NOQA

DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.postgresql",
        "USER": "user",
        "NAME": "django",
        "PASSWORD": "postgres",
        "HOST": "localhost",
        "PORT": 5432,
        "OPTIONS": {
            "server_side_binding": os.getenv("SERVER_SIDE_BINDING") == "1",
        },
    },
    "other": {
        "ENGINE": "django.db.backends.postgresql",
        "USER": "user",
        "NAME": "django2",
        "PASSWORD": "postgres",
        "HOST": "localhost",
        "PORT": 5432,
    },
}

• In tests, run the following:

python runtests.py --settings=test_postgres -k migration_test_data_persistence --parallel=2

An error occurs (for me at least) of the variety:

psycopg.errors.FeatureNotSupported: cannot truncate a table referenced in a foreign key constraint
DETAIL:  Table "model_package_advertisement_publications" references "model_package_publication".
HINT:  Truncate table "model_package_advertisement_publications" at the same time, or use TRUNCATE ... CASCADE.

Running with --parallel=1 does not trigger this issue. The issue triggers for me in Postgres but not with SQLite

This issue was introduced with the fix for #35660 (in commit 060a22ee2dde7aa29a5a29120087c4864887325)

[Simon Charette]

CC'ing Jacob since he worked on #35660.

[Jacob Walls]

Nice catch, looks like I just need to add allow_cascade=True in the sqlflush call in the test setup. ​PR

[Sarah Boyce <42296566+sarahboyce@…>]

In d4b2e06:

Fixed #35921 -- Fixed failure when running tests in parallel on postgres.

Follow-up to a060a22ee2dde7aa29a5a29120087c4864887325.