Search API Solr integration with fivestar (or similar) rating system (fascet and sort)
You can best create a new Entity property in a hook_entity_property_info_alter(), and add a custom field "rating" with a custom getter callback. Like so:

...
      $properties = &amp;$info['flatrow']['properties'];
      $properties['my_indexable_rating_axis_1'] = array(
        'type' =&gt; 'integer',
        'label' =&gt; t('Rating axis 1'),
        'query callback' =&gt; 'entity_metadata_table_query',
        'getter callback' =&gt; 'rating_axis_one_get_properties',
      );
      return $properties;
...


Use it to extend the node entity. The getter callback is where you retrieve the value to be indexed,

function rating_axis_one_get_properties($entity, array $options, $name, $entity_type) {
  $value = $node-&gt;field_fivestar['average_rating']; // I made this up, check how to do it

  return $value;
}


Then index the field with Search API.