Vufind search with variant names from an authority file

[cx6ds]

The option of indexing authority files was built into Vufind many years ago and a journal article was published describing various application scenarios for this collection (https://journal.code4lib.org/articles/5354).

However, one obvious application is missing from this compilation:
Direct catalog searching with variant names in Vufind.

With today's performance, this is possible in Solr with a join query, an example with a variant access point of the poet Friedrich Schiller:

q={!join method=crossCollection from=gnd to=author_GND fromIndex=authority}see_also_keywords:sileris

The following prerequisites are necessary:

1. the collection biblio needs an additional field author_GND. This field contains the identifiers from the authority index.
2. the collection authority needs an additional field gnd.
   Actually identical to id, but with docValues="true”
   
3. the collection authority should have one shard. The collection should have one replication per cloud node

We have tried in various ways to inject this join query as a string into the search, with custom munges and similar to InjectSpellingListener.php

Unfortunately, this did not work.

We would like to have a way to inject such a join parameter into the query.

[demiankatz]

If I were going to tackle this, I would probably start by trying an approach similar to InjectSpellingListener. You say that did not work for you -- could you say a little more about what went wrong? Maybe I can help troubleshoot, or think of a different approach if there's a clear reason why this proved to be unworkable for you!

[cx6ds]

Spellchecking and highlighting are switched on and off via backend parameters.
They are contained in a parameter bag and can therefore be easily controlled via a listener, as they can simply be appended as a key value pair.
The search parameter q, which is sent to Solr, is put together differently.
If we understand correctly we have to extend the VuFindSearch\Backend\Solr\QueryBuilder - Module, what looks like some kind of a cardiac surgery). Have we overlooked any other opportunities?
There we do not see a simple interface where we can insert our addition of the parameter value with a simple string operation at the beginning. The problem is that we are not working at the level of search tokens, but creating a different syntax construct.
Perhaps there is such an interface after all?

[demiankatz]

My thought was that if the join query is just pre-pending a string onto the q parameter that gets generated by the Solr query builder, you could potentially update the ParamBag after the query has been generated, and you wouldn't have to delve too deeply into that logic.

However, if the join fundamentally changes the way the user input is turned into the final Solr query, creating a custom QueryBuilder may be unavoidable.