id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
36468	Popup stays blank after adding a related object when filter_horizontal is used	Juan Rocha		"When using the ""Add another"" popup for a ***ForeignKey field*** in the Django admin and the same ModelAdmin has a ManyToManyField with ***filter_horizontal***, the popup window does not close properly after adding the related object.

Instead, the popup remains open and white (blank), and the browser console throws the following error:

{{{
:8000/static/admin/js/SelectBox.js:60 Uncaught TypeError: Cannot read properties of undefined (reading 'push')
    at Object.add_to_cache (:8000/static/admin/js/SelectBox.js:60:33)
    at :8000/static/admin/j…ctLookups.js:115:31
    at NodeList.forEach (<anonymous>)
    at updateRelatedSelectsOptions (:8000/static/admin/j…ctLookups.js:103:24)
    at dismissAddRelatedObjectPopup (:8000/static/admin/j…ctLookups.js:133:17)
    at popup_response.js:12:16
add_to_cache @ :8000/static/admin/js/SelectBox.js:60
(anonymous) @ :8000/static/admin/j…bjectLookups.js:115
updateRelatedSelectsOptions @ :8000/static/admin/j…bjectLookups.js:103
dismissAddRelatedObjectPopup @ :8000/static/admin/j…bjectLookups.js:133
(anonymous) @ popup_response.js:12
}}}

This seems to be caused by this block in RelatedObjectLookups.js:

{{{
// Update SelectBox cache for related fields.
if (typeof SelectBox !== ""undefined"" && SelectBox.cache[currentSelect.id]) {
    SelectBox.add_to_cache(select.id, option);
    SelectBox.redisplay(select.id);
}
}}}


=== Steps to Reproduce
1. Register a ModelAdmin with:
  * A ForeignKey field (with an ""Add another"" popup)
  * A ManyToManyField using filter_horizontal

2. Click the ""Add another"" button next to the ForeignKey field
3. In the popup, add the new object and submit
4. The popup window stays open with a white screen
5. Console shows a JavaScript error from SelectBox.js


=== Expected Behavior
The popup should close normally and update the original select field with the new object, as it does when filter_horizontal is not present.

=== Workaround
Commenting out or removing the SelectBox.add_to_cache and SelectBox.redisplay lines in RelatedObjectLookups.js avoids the error and restores expected behavior.

=== Version
* Django 5.2.X
* Reproducible in the default admin interface
"	Bug	new	contrib.admin	5.2	Normal		filter_horizontal; SelectBox; add_to_cache;		Unreviewed	0	0	0	0	0	0