Solr facet substring search - solr

Question

Imagine I have the following facets:
Speakers: [Mike Thompson, Thomas Wilkinson, Sally Jeffers]
Venues: [Weill Thomas Medical Center, BB&R Medical Associates, KLR Thompson]
Solr seems to allow a &facet.prefix=Thom where I can get the facets that START with "Thom" and that will return "Speaker: Thomas Wilkinson" but no others.
How can I do the equivalent of &facet.substring=Thom which will return Mike Thompson and Weill Thomas....
I tried &facet.query=Thom but that doesnt seem to work at all.
Thanks

Answer 1

It is not possible to be sure as you did not provide your full query string, but it may be that the facet is not returning Weill Thomas in facet results because you are only specifying facet.field=speakers in your query, and Weill Thomas is actually in the venues field. You would require second facet.field=venues parameter in your search query to retrieve those.
Facet prefix is only used to filter results once the search is already done, so don't use that parameter for searching purposes. Check this question: SOLR facet search by prefix with results highlighting
Edit based on comment:
You don't necessarily need to filter results returned by faceting after the fact, just make sure that only the facets you want match the original query. The facets that were not part of the search query will have 0 occurances on them if you return all facets. You can then set facet.mincount=1 to only get facets that are found within the search results. Here's an example that I mocked up with test data:
q=*Thom*&rows=0&df=speakers&wt=json&indent=true&facet=true&facet.field=speakers&facet.field=venues&facet.mincount=1&json.nl=map
And the response from Solr:
"responseHeader": {
"status": 0,
"QTime": 3,
"params": {
"q": "*Thom*",
"df": "speakers",
"facet.field": [
"speakers",
"venues"
],
"json.nl": "map",
"indent": "true",
"facet.mincount": "1",
"rows": "0",
"wt": "json",
"facet": "true",
"_": "1431772681445"
}
},
"response": {
"numFound": 2,
"start": 0,
"docs": []
},
"facet_counts": {
"facet_queries": {},
"facet_fields": {
"speakers": {
"Mark Thomas": 1,
"Thomas Moore": 1
},
"venues": {
"Weill Thomas": 1
}
},
"facet_dates": {},
"facet_ranges": {},
"facet_intervals": {},
"facet_heatmaps": {}
}

Answer 2

Just wanted to point out a caveat of the proposed solution (i.e. which is to basically just do your facet substring query as the main Solr query, and then the facet values will be what you want). This won't work correctly for multi-valued fields. For example, if a document had 3 values for speaker of "Mark Thomas", "Fred Jones", "John Doe", then the query 'q=*Thom*' would return as facets "Fred Jones" and "John Doe", in addition to "Mark Thomas", and this would not be the desired result (i.e. "Fred Jones" and "John Doe" should not be returned). So for single-valued fields this solution could work, but for multi-valued fields you would probably have to write an intermediary web service that would filter out the non-matches (like "Fred Jones" and "John Doe"). Solr should really add a facet.substring parameter that would work like the facet.prefix parameter, but do substring filtering on the facet values instead of prefix filtering.