How can I tell Solr to return the hit search terms per document?

Question

I have a question about queries in Solr. When I perform a query with multiple search terms that are all logically linked by OR (e.g. q=content:(foo OR bar OR foobar)) than Solr returns a list of documents that all matches any of these terms. But what Solr does not return is which documents were hit by which term(s). So in the example above, what I want to know is which documents in my result list contains the term foo etc. Given this information I would be able to create a term-document matrix.

So my question is: how can I tell Solr to give me that missing piece of information? I'm sure it is somewhere, otherwise the search as a whole would not work. But what am I missing? Thanks for your help.

PS: As a workaround I'm performing a single Solr query for all the search terms. But as you can imagine it's a desaster in matters of performance as the number of search terms can exceed 50 :(

Answer 1

Kind of depends on your requirements, but as far as I know there is no specific support for this in Solr. You can however hack it together in a few other ways. Not sure what you can expect for performance for these, tho..

Use Highlightning

If you use highlighting you can parse the returned highlighted snippets for the start/end tags of the highlighted text. This will be the term that matched something in your query.

Use debugQuery Information

You can parse the information returned by a query with debugQuery=true to determine that a term was associated with a result by looking at termWeight (iirc). This might be a filtered version of your original term (if you have stemming etc. active for the field).

Use Field Collapsing

By using group.query you can build lists of documents that matches each term, instead of issuing several requests. You can also build queries that feature several of the terms OR-ed together if you need lists for "contains either". Might not be effective for a large amount of fields.

Parse the returned document yourself

Get the document, then extract the terms by yourself. Will require a bit of fuzzy matching, since you'll have to deal with text processing on the Solr side as well.

Use Function Queries

You can get metavalues for each document with each term from a FunctionQuery that looks up the number occurences of a term in that document. Will require quite a few function queries for a large number of terms, but might be fast.

.. neither option is perfect, but might work for the problem at hand.