When executing MLT with multiple fields, it should considerem them all

lucene/queries/src/java/org/apache/lucene/queries/mlt/MoreLikeThis.java

@@ -656,13 +656,10 @@ private PriorityQueue<ScoreTerm> createQueue(Map<String, Int> words) throws IOEx
       }
 
       // go through all the fields and find the largest document frequency
-      String topField = fieldNames[0];
-      int docFreq = 0;
-      for (String fieldName : fieldNames) {
-        int freq = ir.docFreq(new Term(fieldName, word));
-        topField = (freq > docFreq) ? fieldName : topField;
-        docFreq = (freq > docFreq) ? freq : docFreq;
-      }
+      String[] array = word.split(":");
+      String fieldName = array[0];
+      word = array[1];
+      int docFreq = ir.docFreq(new Term(fieldName, word));
 
       if (minDocFreq > 0 && docFreq < minDocFreq) {
         continue; // filter out words that don't occur in enough docs
@@ -681,11 +678,11 @@ private PriorityQueue<ScoreTerm> createQueue(Map<String, Int> words) throws IOEx
 
       if (queue.size() < limit) {
         // there is still space in the queue
-        queue.add(new ScoreTerm(word, topField, score, idf, docFreq, tf));
+        queue.add(new ScoreTerm(word, fieldName, score, idf, docFreq, tf));
       } else {
         ScoreTerm term = queue.top();
         if (term.score < score) { // update the smallest in the queue in place and update the queue.
-          term.update(word, topField, score, idf, docFreq, tf);
+          term.update(word, fieldName, score, idf, docFreq, tf);
           queue.updateTop();
         }
       }
@@ -741,7 +738,7 @@ private PriorityQueue<ScoreTerm> retrieveTerms(int docNum) throws IOException {
           }
         }
       } else {
-        addTermFrequencies(termFreqMap, vector);
+        addTermFrequencies(termFreqMap, vector, fieldName);
       }
     }
 
@@ -773,7 +770,7 @@ private PriorityQueue<ScoreTerm> retrieveTerms(Map<String, Collection<Object>> f
    * @param termFreqMap a Map of terms and their frequencies
    * @param vector List of terms and their frequencies for a doc/field
    */
-  private void addTermFrequencies(Map<String, Int> termFreqMap, Terms vector) throws IOException {
+  private void addTermFrequencies(Map<String, Int> termFreqMap, Terms vector, String fieldName) throws IOException {
     final TermsEnum termsEnum = vector.iterator();
     final CharsRefBuilder spare = new CharsRefBuilder();
     BytesRef text;
@@ -786,10 +783,11 @@ private void addTermFrequencies(Map<String, Int> termFreqMap, Terms vector) thro
       final int freq = (int) termsEnum.totalTermFreq();
 
       // increment frequency
-      Int cnt = termFreqMap.get(term);
+      String mapKey = fieldName + ":" + term;
+      Int cnt = termFreqMap.get(mapKey);
       if (cnt == null) {
         cnt = new Int();
-        termFreqMap.put(term, cnt);
+        termFreqMap.put(mapKey, cnt);
         cnt.x = freq;
       } else {
         cnt.x += freq;
@@ -826,9 +824,10 @@ private void addTermFrequencies(Reader r, Map<String, Int> termFreqMap, String f
         }
 
         // increment frequency
-        Int cnt = termFreqMap.get(word);
+        String mapKey = fieldName + ":" + word;
+        Int cnt = termFreqMap.get(mapKey);
         if (cnt == null) {
-          termFreqMap.put(word, new Int());
+          termFreqMap.put(mapKey, new Int());
         } else {
           cnt.x++;
         }

lucene/queries/src/test/org/apache/lucene/queries/mlt/TestMoreLikeThis.java

@@ -53,6 +53,13 @@ public void setUp() throws Exception {
     RandomIndexWriter writer = new RandomIndexWriter(random(), directory);
 
     // Add series of docs with specific information for MoreLikeThis
+    Document doc = new Document();
+    doc.add(newTextField("text", "lucene", Field.Store.YES));
+    doc.add(newTextField("foobar", "foobared", Field.Store.YES));
+    doc.add(newTextField("text", "bar", Field.Store.YES));
+    doc.add(newTextField("foobar", "bar", Field.Store.YES));
+    writer.addDocument(doc);
+
     addDoc(writer, "lucene");
     addDoc(writer, "lucene release");
     addDoc(writer, "apache");
@@ -80,6 +87,7 @@ private void addDoc(RandomIndexWriter writer, String[] texts) throws IOException
     Document doc = new Document();
     for (String text : texts) {
       doc.add(newTextField("text", text, Field.Store.YES));
+      doc.add(newTextField("foobar", text, Field.Store.YES));
     }
     writer.addDocument(doc);
   }
@@ -152,7 +160,17 @@ public void testMultiFields() throws Exception {
     mlt.setMinTermFreq(1);
     mlt.setMinWordLen(1);
     mlt.setFieldNames(new String[] {"text", "foobar"});
-    mlt.like("foobar", new StringReader("this is a test"));
+
+    BooleanQuery query = (BooleanQuery) mlt.like(0);
+    Collection<BooleanClause> clauses = query.clauses();
+    assertEquals("Expected 4 clauses only!", 4, clauses.size());
+    for (BooleanClause clause : clauses) {
+      Term term = ((TermQuery) clause.getQuery()).getTerm();
+      assertTrue(Arrays.asList(new Term("text", "lucene"),
+                               new Term("foobar", "foobared"),
+                               new Term("text", "bar"),
+                               new Term("foobar", "bar")).contains(term));
+    }
     analyzer.close();
   }