Boosting for MoreLikeThisHandler

[Tom Morton]

Hi,
   SOLR-295 <https://issues.apache.org/jira/browse/SOLR-295> mentions boost
support for morelikethis and then seems to have been subsumed by
SOLR-281<https://issues.apache.org/jira/browse/SOLR-281>but I don't
think this got implemented.  I've patched MoreLikeThisHandler to
support this.  Here's a summary of the approach:


   -   Parse out "mlt.qf parameters" to get boosts in dismax like format
   (existing code from DisMax param parse code used to produce a
   Map<String,Float>)
   -   Iterate through mltquery terms, get boost by looking at field from
   which mltquery term came,  and multiply boost specified in map by existing
   term boost.
      - If mlt.boost=false, then you get the same boost values as in
      map/mlt.qf parameters,
   - If mlt.boost=true then you get normalized boost multiplied by specified
      boost (which makes sense to me).


Patch attached.

Should I re-open either SOLR-281 or SOLR-295 (if I can) or create a new jira
ticket for this?

Thanks...Tom

Index: src/java/org/apache/solr/common/params/MoreLikeThisParams.java
===================================================================
--- src/java/org/apache/solr/common/params/MoreLikeThisParams.java	(revision 663326)
+++ src/java/org/apache/solr/common/params/MoreLikeThisParams.java	(working copy)
@@ -35,6 +35,7 @@
   public final static String MAX_QUERY_TERMS       = PREFIX + "maxqt";
   public final static String MAX_NUM_TOKENS_PARSED = PREFIX + "maxntp";
   public final static String BOOST                 = PREFIX + "boost"; // boost or not?
+  public final static String QF                    = PREFIX + "qf"; //boosting applied to nlt fields
 
   // the /mlt request handler uses 'rows'
   public final static String DOC_COUNT = PREFIX + "count";
Index: src/java/org/apache/solr/handler/MoreLikeThisHandler.java
===================================================================
--- src/java/org/apache/solr/handler/MoreLikeThisHandler.java	(revision 663326)
+++ src/java/org/apache/solr/handler/MoreLikeThisHandler.java	(working copy)
@@ -23,8 +23,11 @@
 import java.net.URL;
 import java.util.ArrayList;
 import java.util.Comparator;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Map;
+import java.util.Set;
 import java.util.regex.Pattern;
 
 import org.apache.lucene.document.Document;
@@ -37,6 +40,7 @@
 import org.apache.lucene.search.similar.MoreLikeThis;
 import org.apache.solr.common.SolrException;
 import org.apache.solr.common.params.CommonParams;
+import org.apache.solr.common.params.DisMaxParams;
 import org.apache.solr.common.params.FacetParams;
 import org.apache.solr.common.params.MoreLikeThisParams;
 import org.apache.solr.common.params.SolrParams;
@@ -51,7 +55,6 @@
 import org.apache.solr.schema.IndexSchema;
 import org.apache.solr.schema.SchemaField;
 import org.apache.solr.search.DocIterator;
-import org.apache.solr.search.DocSet;
 import org.apache.solr.search.DocList;
 import org.apache.solr.search.DocListAndSet;
 import org.apache.solr.search.QueryParsing;
@@ -231,6 +234,7 @@
     final IndexReader reader;
     final SchemaField uniqueKeyField;
     final boolean needDocSet;
+    Map<String,Float> boostFields;
     
     Query mltquery;  // expose this for debugging
     
@@ -260,12 +264,25 @@
       mlt.setMaxQueryTerms(     params.getInt(MoreLikeThisParams.MAX_QUERY_TERMS,       MoreLikeThis.DEFAULT_MAX_QUERY_TERMS));
       mlt.setMaxNumTokensParsed(params.getInt(MoreLikeThisParams.MAX_NUM_TOKENS_PARSED, MoreLikeThis.DEFAULT_MAX_NUM_TOKENS_PARSED));
       mlt.setBoost(            params.getBool(MoreLikeThisParams.BOOST, false ) );
+      boostFields = SolrPluginUtils.parseFieldBoosts(params.getParams(MoreLikeThisParams.QF));
     }
     
+    private void setBoosts(Query mltquery) {
+      List clauses = ((BooleanQuery)mltquery).clauses();
+      for( Object o : clauses ) {
+        TermQuery q = (TermQuery)((BooleanClause)o).getQuery();
+        Float b = this.boostFields.get(q.getTerm().field());
+        if (b != null) {
+          q.setBoost(b*q.getBoost());
+        }
+      }
+    }
+    
     public DocListAndSet getMoreLikeThis( int id, int start, int rows, List<Query> filters, List<InterestingTerm> terms, int flags ) throws IOException
     {
       Document doc = reader.document(id);
       mltquery = mlt.like(id);
+      setBoosts(mltquery);
       if( terms != null ) {
         fillInterestingTermsFromMLTQuery( mltquery, terms );
       }
@@ -289,6 +306,7 @@
     public DocListAndSet getMoreLikeThis( Reader reader, int start, int rows, List<Query> filters, List<InterestingTerm> terms, int flags ) throws IOException
     {
       mltquery = mlt.like(reader);
+      setBoosts(mltquery);
       if( terms != null ) {
         fillInterestingTermsFromMLTQuery( mltquery, terms );
       }