Sort by popularity: is this how to do it?

Ok, i added a new is_totalcount field to the index and made sure apachesolr_views was able to use it for sorting...

/*
   hook_apachesolr_update_index() modifies the $document object before
   indexing.
*/
function mymodule_apachesolr_update_index(&$document, $node) {
	// Record the node's number of page views, if available
	if (module_exists('statistics')) {
		$stats = statistics_get($node->nid);
		if ($stats['totalcount']) {
			$document->is_totalcount = $stats['totalcount'];
		}
	}
}


/*
   hook_apachesolr_prepare_query() runs before hook_apachesolr_modify_query(),
   before query is statically cached. New sorts must be added at this point.
*/
function mymodule_apachesolr_prepare_query(&$query) {
  $query->set_available_sort('is_totalcount', array(
    'title' => t('Total views count'),
    'default' => 'desc',
  ));
}


/**
 * Implementation of hook_views_data_alter()
 *
 * Make available new fields and sorts to views
 */
function mymodule_views_data_alter(&$data) {
	$data['apachesolr_node']['is_totalcount'] = array(
		'title' => t('Total views count'),
		'help' => t('The total views count for this node.'),
		'field' => array(
			'handler' => 'views_handler_field_numeric',
			'click sortable' => TRUE,
		),
		'sort' => array(
			'handler' => 'apachesolr_views_handler_sort',
		),
    );
}

Now when i sort by is_totalcount using the exposed form, the GET request to Solr contains: sort=sort_title+asc,created+desc,is_totalcount+desc. Brilliant!

But the is_totalcount is last in the list, rather than first, so it still has no effect. I've just noticed that this also happens for the the "created" sort field too. The sort ordering in the GET request never changes! I wonder if this is a bug, or is this a unicorny feature?

I made a quick patch to the apachesolr_views module to allow changing the priority of sorting. Very simple change in apachesolr_views/apachesolr_views_query.inc:

  function set_solrsort($field, $direction) {
	// Patch to force only one sort (since there isn't yet a way to set the priority of multiple sort fields)
	//$this->add_sort($field, $direction);
	$this->_sorts = array();
	$this->_sorts[$field] = strtolower($direction);
  }

Then in your custom module you'd have something like...

function mymodule_apachesolr_modify_query(&$query, &$params) {
	// This doesn't actually do anything yet, but it's recommended
	$query->set_available_sort('is_totalcount', array(
		'title' => t('Total views count'),
		'default' => 'desc',
	));

	
	// Use this for normal views exposed filters
	//if (isset($_GET['sort_by'])&& isset($_GET['sort_order']))
	//	$query->set_solrsort(check_plain($_GET['sort_by']), check_plain($_GET['sort_order']));

	// And this if you're using the Better Exposed Filters module
	if (isset($_GET['sort_bef_combine'])) {
		$befcombine = check_plain($_GET['sort_bef_combine']);
		$sort = explode(' ', $befcombine);
		if (count($sort)==2) {
			$query->set_solrsort($sort[0], $sort[1]);
		}
	}
}

I would have used mymodule_apachesolr_prepare_query() instead of mymodule_apachesolr_modify_query(), but the prepare query hook didn't seem to be working for me :( Anyway i hope this is of help to someone, since sorting is surely extremely popular when doing a search. Maybe the apachesolr_views module will one day allow this so we don't need the patch?

NOTE: tested with D6.22, Views 6.x-3.0+67-dev, Apache Solr Search 6.x-1.5, Apache Solr Views Integration 6.x-1.x-dev, Better Exposed Filters 6.x-3.x-dev.
++NOTE: If you don't want to patch the apachesolr_views module, i see these people have found a more elaborate route (which is a bit of a kludge).