#23641: Apps.set_installed_apps causes signals registered with apps as senders
not
to be received
------------------------------+--------------------
Reporter: wrwrwr | Owner: nobody
Type: Bug | Status: new
Component: Core (Other) | Version: master
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
------------------------------+--------------------
Calling `Apps.set_installed_apps` before `DiscoverRunner.setup_databases`
causes pre/post_migrate signal handlers registered on module import with
app configs as senders not to be executed for the test database.
The signal dispatcher stores `id()` of the sender argument provided to
`connect` to identify the sender that we're interested in receiving the
signals from, in case of `post_migrate` signals this is often an id of an
`AppConfig` for the registering app. When `set_installed_apps` is called
it reinstantiates all app configs. If afterwards you send a signal using
app config from the global app registry as the sender (as is the case in
`emit_post_migrate_signal` when setting up test databases), its id won't
match the one stored by the dispatcher, thus signal handlers won't get
executed.
[https://github.com/wrwrwr/django/tree/fix/missing-default-site-with-set-
installed-apps A branch] with an example test case and a possible partial
fix (that in full would be moving all module-level signal registration to
`AppConfig.ready`).
[https://github.com/wrwrwr/mezzanine/blob/maintenance/1.8-discover-test-
runner/mezzanine/utils/tests.py#L117 A sketch] of a possible more general
solution / workaround (this Mezzanine wrapper for `DiscoverRunner` turned
out pretty involved, you're welcome to suggest a cleaner implementation
:-)
See also #22688: AppConfig.ready is going to get called for every
instance, so should be a good place to put these signal registrations.
--
Ticket URL: <https://code.djangoproject.com/ticket/23641>
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