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Rebuild cached model relations when installing extension apps.
Review Request #15219 — Created Aug. 7, 2026 and updated
We currently have a bug where a model's relation tree can be cached before
an extension providing a related model is registered, leaving the relation
permanently missing from it.Django's
Apps.set_installed_apps()setsApps.readytoFalsebefore both
of its calls toApps.clear_cache()(its own, and the one at the end of
Apps.populate()). Howeverclear_cache()only expires the per-model
Optionscaches when the registry is ready. Installing an app therefore
never rebuilds those cached relation trees.This bug is exposed when an extension imports something from another extension
at module scope. For example, an extension that uses Power Pack's User Roles
in an approval hook will likely import the user role model at the module scope
(we do this in an example in Review Board's documentation). The extension
manager imports every extension's module before initializing any of them, so
in this case the related model gets registered but is unreachable through
AppConfig. Then if something accesses the model's relation tree before the
extensions are registered, the tree is cached without the extension model's
relation. This was bug was discovered when trying to import User Roles in
RBCommons' team admin code.This change makes
ExtensionManager._add_to_installed_apps()clear the cache
itself, so that model relations can be properly populated.
- Ran unit tests.
- Saw the
FieldErrorI was getting in RBCommons from the User Roles
relation being missing go away.
| Summary | ID |
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| 5d5cec0b844399cd92d0b056dcc664e7bc0df23d |
| Description | From | Last Updated |
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I worry a little that future us will see that set_installed_apps() clears caches and we'll remove this line. Can we … |
david
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This might be a little clearer as "Access the relation tree now, both to sanity-check that the relation is absent … |
david
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This seems a little overly complicated. How about: self.assertEqual(user.test_extension_related_models.count(), 1) Same for the check at the end of this method. |
david
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Can we add one more assertion between these two lines to verify that disabling removes the relation? self.extension_mgr.disable_extension(extension.id) self.assertNotIn('test_extension_related_models', {f.name … |
david
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I worry a little that future us will see that
set_installed_apps()clears caches and we'll remove this line. Can we be a little more explanatory in the mechanics?# Django's set_installed_apps() calls clear_cache() twice (its own, # and the one at the end of populate()), but both run while # Apps.ready is False. clear_cache() only calls _expire_cache() on # each model when the registry is ready, so neither call rebuilds # the per-model caches. # # Without this, a model's relation tree may have been cached before # an extension providing a related model was registered, leaving # that relation permanently missing from the tree. -
This might be a little clearer as "Access the relation tree now, both to sanity-check that the relation is absent and to warm the cache for the tree in that state."
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This seems a little overly complicated. How about:
self.assertEqual(user.test_extension_related_models.count(), 1)Same for the check at the end of this method.
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Can we add one more assertion between these two lines to verify that disabling removes the relation?
self.extension_mgr.disable_extension(extension.id) self.assertNotIn('test_extension_related_models', {f.name for f in User._meta.get_fields()}) self.extension_mgr.enable_extension(extension.id)