def to_solr (solr_doc = {})
    facetable = Solrizer::Descriptor.new(:string, :indexed, :multivalued)
    Solrizer.insert_field(solr_doc, 'type', 'Collection')
    Solrizer.insert_field(solr_doc, 'type', 'Collection',facetable)
    Solrizer.insert_field(solr_doc, 'type', 'ProvenanceCollection')