Support the multi-select facet feature of Solr where the associated counts are maintained as if no contraints have been applied

btw. if anything on this is server/backend dependent: i'm using search api with apache solr 1.41.

Yep, Chris, looks like #1421564 is addressing the same problem.

hm, is it really that easy?
Consider the following basic case:
There are two facets, "category" and "country", and both theirs items should keep their count, i.e. their facet items result count should reflect the filtering constraints of each other facet, but not the current filtering contraint of their own facet.
Can this by accomplished using a single solr query with tags on the field/facets ?
I mean: Wouldn't that make the counts in the example independent of _all_ facet filtering contraints (and not just independent of the own facet's filtering contraints, viewed from the perspective of a facet item and its count)?

Forget it, because:

YESSSSS !!!! It's alive!!!! And working!
Well, not as a general FacetAPI Implementation, but the following code simulates the suggested tagging and tagged-excluding on solr queries made by search_api with search_api_solr, on all involved facets for a certain search_api index. See it as a proof of (the tagging) concept, and/or change it (module name, limiting index name etc.) and use it to solve your (anyone) problem:

/*
 * Implementes _search_api_solr_query_alter().
 *
 * Add tags to fq fields and facet.field fields to exclude each facet's
 * filtering contraints from influencing its own facet item's result counts,
 * to always keep the result counts of each facet item independent of that
 * facet's filtering.
 *
 * See http://drupal.org/node/1446824# for background information.
 */
function ri_portfolio_search_api_solr_query_alter(array &$call_args, SearchApiQueryInterface $query) {
  // Only alter queries on the portfolio index.
  if ($query->getIndex()->machine_name != 'portfolio') return;

  // Go through all facet.field(s).
  foreach($call_args['params']['facet.field'] as $key => $facetfield) {
    // Come up with tag name for the facet.field.
    $tag = 'dtex'.$key;
    // Mark the tag form "exclude from counting" for this facet.
    $call_args['params']['facet.field'][$key] = "{!ex=$tag}" . $facetfield;
    // Tag the respective query field with the tag.
    _ri_portfolio_alter_solr_add_field_tag($call_args, $facetfield, $tag);
    
    // What the heck is done here? See example and explanation at:
    // Example from http://drupal.org/node/1446824#comment-5632892
    // q=mainquery&fq=status:public&fq=doctype:pdf&facet=on&facet.field=doctype
    // q=mainquery&fq=status:public&fq=         doctype:pdf&facet=on&facet.field=        doctype
    // q=mainquery&fq=status:public&fq={!tag=dt}doctype:pdf&facet=on&facet.field={!ex=dt}doctype
  }  
}


/**
 * Helper function to add a tag to a solr query field for search_api_solr query.
 */
function _ri_portfolio_alter_solr_add_field_tag(array &$call_args, $change_fieldname, $tag) {
  foreach($call_args['params']['fq'] as $key => $field) {
    $fieldname_end_pos = strpos($field, ':');
    $fieldname = substr($field, 0, $fieldname_end_pos);
    if ($fieldname == $change_fieldname) {
      $call_args['params']['fq'][$key] = "{!tag=$tag}" . $field;
    }
  }
}

Thanks Chris for the - as always - crucial hints!! And thanks heacu for the initial suggestion/idea at http://drupal.org/node/1431926#comment-5582734 !

So, how are we going to make this happen in a generic way in apachesolr.module / search_api_solr,module?

Issue for support in search_api(_solr) opened at #1449336: Support multi-select facets with item counts independent of own facet.