Handle OR/AND switch leading to empty results

[malberts]

Multiple OR values can be used to get a non-empty search result. When switching that same filter from OR to AND, it can result in an empty search result. The same selection would not have been possible if the filter was set to AND in the first place, since the additional values would've been removed. The UI does not show the selected values, so user is now unable to easily undo the change.

Screencast_20250211_023317.mp4

A possible solution would be to show the selected values, even when they would technically have 0 counts based on the current search. Then the user can try to deselect values until it leads to a non-empty search result.

Related: removing filters when they have no values and no values were selected: #176

[JeroenDeDauw]

Is this done?

[malberts]

No. #176 hides actually empty filters (i.e. nothing selected), and indirectly ends up hiding the non-empty filters here (i.e. something selected, but leads to empty result). We still need a way to deselect selected values where the current selection leads to an empty result.

[alistair3149]

The challenge is that when the facet is in AND mode, it has no visibility of what values are in OR mode previously.
The two approaches that I can think of are either persisting the values of the last query, or run a separate query to get the values in OR mode. The second way isn't optimal and I am not sure how the first approach can be done optimally.

If there isn't a good way to handle this, I would suggest deselecting all values in the facet when clicking on the toggle. At the very least it will avoid the "impossible" query that we have with this case.

[malberts]

I don't think there needs to be explicit tracking of what mode it was in.

We know what values were selected here (in $state):

WikibaseFacetedSearch/src/Presentation/ListFacetHtmlBuilder.php

Lines 33 to 37 in da2a534

	public function buildHtml( FacetConfig $config, PropertyConstraints $state ): string {
	$valueCounts = $this->getValuesAndCounts( $config );
	if ( count( $valueCounts ) === 0 ) {
	return '';
	}

My idea is if $valueCounts is empty AND $state contains selected values, then we can use a new ZeroValueCounter (or likely just a method) that simply returns 0 counts for a list of provided item ids.

See #249