Dynamically created connection are disallowed in SimpleTestCase and subclasses.

[Florian Apolloner]

While working on connection pooling for postgres I ran into the following regression (since 8fb0be3500cc7519a56985b1b6f415d75ac6fedb):

from django.db import connection
from django.test import TestCase


class Test(TestCase):
    def test_something(self):
        new_connection = connection.copy("asd")
        with new_connection.cursor() as cursor:
            print(cursor.execute("SELECT 1").fetchall())

On 5.0 this works fine, on main this fails with:

django.test.testcases.DatabaseOperationForbidden: Database threaded connections to 'asd' are not allowed in this test. Add 'asd' to test_regression.Test.databases to ensure proper test isolation and silence this failure.

I cannot really add this to databases since this is a dynamically created database. I am opening this as release blocker so it doesn't get lost (I might be holding it wrong though)

[Mariusz Felisiak]

TBH, I don't see how we could handle this and keep 8fb0be3500cc7519a56985b1b6f415d75ac6fedb. The main question is, do we want to support something like this? Creating a copy of the connection copy is tricky, and if you change the alias in the meantime it becomes even more complicated.

[Florian Apolloner]

Well I will see if I can get around it without an alias change in the pool tests, but testing the pooling stuff is tricky without creating completely new connections :D

[Mariusz Felisiak]

We could ignore dynamically created connections, e.g.:

django/test/testcases.py

@@ -280 +280 @@
                 self.connection is None
                 and self.alias not in cls.databases
                 and self.alias != NO_DB_ALIAS
+                and self.alias in connections
             ):
                 # Connection has not yet been established, but the alias is not allowed.
                 message = cls._disallowed_database_msg % {

What do you think?

[Florian Apolloner]

That seems like a workable solution to me if it doesn't conflict with what you have been trying to achieve in the first place 👍

[Mariusz Felisiak]

Replying to Florian Apolloner:

That seems like a workable solution to me if it doesn't conflict with what you have been trying to achieve in the first place 👍

Thanks, let's try.

[Mariusz Felisiak]

​PR

[GitHub <noreply@…>]

In 5f637a8a:

Fixed #35226 -- Reallowed executing queries for dynamically created connections.

Regression in 8fb0be3500cc7519a56985b1b6f415d75ac6fedb.

Thanks Florian Apolloner for the report.