title: Restrict multi field facet calculation to subset of possible values
body: <p>I have a non trivial SOLR query, which already involves a filter query and facet calculations over multiple fields. One of the facet fields is a a multi value integer field, that is used to store categories. There are many possible categories and new ones are created dynamically, so using multiple fields is not an option.</p>
  
  <p>What I want to do, is to restrict facet calculation over this field to a certain set of integers (= categories). So for example I want to calculate facets of this field, but only taking categories 3,7,9 and 15 into account. All other values in that field should be ignored.</p>
  
  <p>How do I do that? Is there some build in functionality which can be used to solve this? Or do I have to write a custom search component?</p>