Add title to doc script for bucketing es6 responses

oaipmh-core/src/main/java/info/textgrid/middleware/SetDeliverer.java

@@ -124,8 +124,9 @@ public class SetDeliverer {
     // Assemble DH ES request.
     else if (this.dariah) {
 
-      Script collectionID = new Script("doc['administrativeMetadata.dcterms:identifier']");
-      
+      Script mergeCollectionIDAndTitle = new Script(
+          "doc['administrativeMetadata.dcterms:identifier'].value + '&' + doc['descriptiveMetadata.dc:title']");
+
       // Do filter all collections (via descriptiveMetadata.dc:format) AND
       // get out all the child objects and collections (NO descriptiveMetadata.dc:relation),
       // so we get exactly one set per root collection only!
@@ -138,7 +139,7 @@ public class SetDeliverer {
       AggregationBuilder collectionFilterTerm =
           AggregationBuilders.terms(DH_COLLECTION_FILTER_TERM_NAME)
               .field("administrativeMetadata.dcterms:identifier")
-              // .script(collectionID)
+              .script(mergeCollectionIDAndTitle)
               .size(DH_SIZE);
 
       collectionFilter.subAggregation(collectionFilterTerm);