An example SOLR query component to pull other objects

Consider Linked-in example. i.e. I have a set of connections. With single SOLRrequest, following SOLR component brings all first level connections information. In RDBMS world, typical example is employee table. i.e. bring me first level employees of manager. Assume single table contains both employee and manager information. (typical Adjacency list)

In terms of physical SOLR mapping, every document contains a connection field which contains the list(Adjacency list) of connections (root ids)

Configuration point of view, add the following to solrconfig.xml

public class ExampleComponent extends SearchComponent
{
  public static final String COMPONENT_NAME = "example";

  @Override
  public void prepare(ResponseBuilder rb) throws IOException
  {
  
  }
  @SuppressWarnings("unchecked")
  @Override
  public void process(ResponseBuilder rb) throws IOException
  {
     DocSlice slice = (DocSlice) rb.rsp.getValues().get("response");
       SolrIndexReader reader = rb.req.getSearcher().getReader();
       SolrDocumentList rl = new SolrDocumentList();
       int docId=0;//// at this point consider only one rootid.
       for (DocIterator it = slice.iterator(); it.hasNext(); ) {
         docId = it.nextDoc();
         Document doc = reader.document(docId);
         String id = (String)doc.get("id");
         String connections = (String)doc.get("contains");
         System.out.println("\n id:"+id+" contains-->"+connections);
         List<String> list = new ArrayList<String>();
         list.add(id);//add rootid too. If we have joins in solr4.0
   int pos = 0, end;
   while ((end = connections.indexOf(',', pos)) >= 0) {
    list.add(connections.substring(pos, end));
    pos = end + 1;
   }
   BooleanQuery bq = new BooleanQuery();
   Iterator<String> cIter = list.iterator();
   while (cIter.hasNext()) {
    String anExp = cIter.next();
    TermQuery tq = new TermQuery(new Term("id",anExp));
    bq.add(tq, BooleanClause.Occur.SHOULD);
   }
         SolrIndexSearcher searcher = rb.req.getSearcher();
         DocListAndSet results = new DocListAndSet();
         results.docList = searcher.getDocList(bq, null, null,0, 100,rb.getFieldFlags());
         System.out.println("\n results.docList-->"+results.docList.size() );
         rl.setNumFound(results.docList.size());
         rb.rsp.getValues().remove("response");
         rb.rsp.add("response", results.docList);
     }
  }

  @Override
  public String getDescription() {
    return "Information";
  }
  @Override
  public String getVersion() {
    return "Solr gur";
  }
  @Override
  public String getSourceId() {
    return "Satya Solr Example";
  }
  @Override
  public String getSource() {
    return "$URL:   }
  @Override
  public URL[] getDocs() {
    return null;
  }
}