The hibernate-search facet search API is pretty amazing but it lacks a little on the following:
- Facet-Count values are incorrect where a facet matches a fields that have multiple values. I.e. the facet-counts are correct where the facet has a 1-to-many relationship with result-set items but the facet-counts are entirely incorrect where the facet has a many-to-many relationship with result-set items.
The facet-count values are that of the number of matched result-set items within the result-set as distinct from the number of matched result-set items that will be merged into the result-set if the facet is applied. This is highly undesirable where more than one facet-group is used conjunctively. Let’s explain…
- Facet-counts are available before any facets are applied. Adjusted facet-counts are available after facets are applied. This is great because it facilitates two different usages. With the former, the facet-counts can remain static as facets are selected and deselected. With the latter, applying one facet will reduce the facet-count for other facets. In fact, the other facet-counts can reduce to zero. This zero count does not necessarily mean no result-set items will result from applying the facet. Consequently, we don’t know if clicking on the facet will yield new results or not. If a facet yields no results, and it is used in conjunction with facets from another facet group, this can lead to a zero-results situation. Confused? no problem Ok, allot of detail, description, example and analysis is provided in this blog.
These issues are identified in the following discussion threads:
- This blog delivers a comprehensive solution to all issues surrounding facet-counts in hibernate-search. The solution is derived from the information provided here: http://sujitpal.blogspot.ie/2007/04/lucene-search-within-search-with.html. A java class that delivers the solution is provided. There is also a fully working maven project demonstrating the solution in action.