: If you do need to implement something truely custom, writing it as your : own QParser to trigger via an "fq" can be advantageous so it can cached : and re-used by many queries.
I forgot to mention a very cool new feature that is about to be released in Solr 3.4 You can now instruct Solr that an "fq" filter query should not be cached, in which case Solr will only consult it after executing the main query -- which can be handy if you have some filtering logic that is very expensive to compute for each document, and you only wnat to evaluate for documents that have already been matched by the main query and all other filter queries. Details are on the wiki... https://wiki.apache.org/solr/CommonQueryParameters#Caching_of_filters -Hoss
