Boosting boolean fields in Solr - sorting

Question

Is it possible to boost boolean fields in Solr so that they receive a higher score?
We've got an index which looks a bit like this:
document_id
title
description
keywords
is_reviewed
When searching, documents that have been reviewed (ie. is_reviewed = true) should be weighted more heavily than those that haven't, rather than exclude them completely.
Using is_review:true^100 doesn't seem to work, and excludes unreviewed items instead of just giving them a lower weighting. If there a different way this can be achieved? Thanks!

Answer 1

Some query parsers have a feature dedicated to this kind of usage. For example, the dismax query parser has a boost query bq which allows you to boost documents which match a query by adding its clauses to the original query. There is also a boost function bf which allows you to multiply scores by the result of a function. For example, using is_review as this bf parameter,
the score of every document whose is_review field is undefined will be multiplied by 0.
the score of every document so that is_review=false will be multiplied by one.
the score of every documentso that is_review=true will be multiplied by two.
is_review:true^100 shouldn't exclude non reviewed items unless you are using AND as the default query operator. In this case, you could try to replace is_review:true^100 by (is_review:true^100 OR is_review:false^0).
If you are interested in the boost feature of the dismax query parser but would like to stick to the default query parser, you can use the boost query parser which will allow you to multiply the scores of any query with any function.

Answer 2

Drupal
Here is the solution for those who're using Drupal CMS.
First, find your field name in Schema Browser at /solr/admin/schema.jsp
Then, depending on the module which you use, try the following examples:
Apachesolr module
Code example:
/**
* Implements hook_apachesolr_query_alter().
*/
function hook_apachesolr_query_alter(DrupalSolrQueryInterface $query) {
$query->addParam('bq', array('is_review' =>
'(is_review:true^100 OR is_review:false^0)'
));
}
Search Solr API module
Code example:
/**
* Implements hook_search_api_solr_query_alter().
*/
function hook_search_api_solr_query_alter(&$call_args, SearchApiQueryInterface $query) {
$call_args['params']['bq'][] = '(is_review:true^100 OR is_review:false^0)';
}