Hierarchical Facet Search

[bradenmacdonald]

Hi!

I'm trying to build a search experience like this using Meilisearch, where there are hierarchical tags used to categorize content. The tags come from external taxonomies and there could be thousands of tags in each taxonomy, so we want a way for users to be able to search in the "tags" filter before checking/unchecking tags to filter by.

I was hoping that the "Searching facet values" feature would support this, but it doesn't seem to work for this use case at all.

For context, we have the hierarchical tags denormalized into several fields as recommended in the guide: tags.level0, tags.level1, tags.level2, tags.level3, etc. This works great for basic filtering and since I specified tags as a filterable attribute when creating the index, I can do basic filtering using the tags. It also works with Instansearch's HierarchicalMenu widget, though we had to replace it with a custom implementation because their widget only allows selecting a single tag at a time.

However, here are the problems:

1. It seems like it's not possible to do a keyword search on the hierarchical facets - if I call client.index(indexName).searchForFacetValues({ facetName: "tags", facetQuery: "..." }); then Meilisearch gives empty results (which I guess is expected, because the API doesn't even have a way to express nested taxonomy values in the result from this API call). And if I call searchForFacetValues with facetName: "tags.level0", it gives an error that "Attribute tags.taxonomy is not facet-searchable. To make it facet-searchable add it to the filterableAttributes index settings." This seems inconsistent with how filtering works in general, because for all other API methods, I only needed to include tags in the filterableAttributes and it allows me to filter and facet on all the sub-fields of tags. I did try adding tags.level0 etc. to filterableAttributes, and it does work, but this is still problematic because I want to search the whole tree of hierarchical facets, and I would have to make at least four separate API calls to search each level and then combine the results.
2. Even when searchForFacetValues does work, it's far too limited for our use case. As you can see in the screenshot, there are many tags with multiple words in the name, and searchForFacetValues only allows searching on the first word - which would be a confusing and broken experience for users.

So, I guess this is a feature request for two things:

1. Allow searchForFacetValues to search sub-fields like tags.level0 and tags.level1 simultaneously.
2. Allow better keyword search on facet values. I would prefer it work just as if I did a regular query on the tags compound field; for example, .search("Middle Word", { attributesToSearchOn: ["tags.level0", "tags.level1", ...]}) will match text from the middle of the facet names; the only problem with this approach is that it's not possible to combine with an existing overall query keyword, like the searchForFacetValues field allows.

Relates to:

• https://roadmap.meilisearch.com/c/97-nested-facets
• https://blog.meilisearch.com/nested-hierarchical-facets-guide/
• https://github.com/orgs/meilisearch/discussions/544

[macraig]

Hi @bradenmacdonald , apologies for the delayed response. We've opened an issue to investigate the behavior you mentioned here: meilisearch/meilisearch#4638

[bradenmacdonald]

Thanks @macraig. I commented on that issue too.

For reference, here is the code I ended up writing to search hierarchichal facets in a "best effort" fashion, despite the current limitations of the Meilisearch API: https://github.com/openedx/frontend-app-course-authoring/blob/732b7ed86cb3845fbed0471a217c065c14091b3b/src/search-modal/data/api.js#L318-L388
I would definitely prefer a "proper" solution that does a facet search rather than this attempt to reconstruct the matching facets on the frontend.