Create only one MLT query per field for all queried items

src/main/java/org/elasticsearch/common/lucene/search/MoreLikeThisQuery.java

@@ -27,11 +27,13 @@
 import org.apache.lucene.search.similarities.DefaultSimilarity;
 import org.apache.lucene.search.similarities.Similarity;
 import org.apache.lucene.search.similarities.TFIDFSimilarity;
+import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.FastStringReader;
 
 import java.io.IOException;
 import java.io.Reader;
 import java.util.Arrays;
+import java.util.List;
 import java.util.Set;
 
 /**
@@ -174,13 +176,17 @@ public String[] getLikeTexts() {
     }
 
     public void setLikeText(String likeText) {
-        this.likeText = new String[]{likeText};
+        setLikeText(new String[]{likeText});
     }
 
     public void setLikeText(String... likeText) {
         this.likeText = likeText;
     }
 
+    public void setLikeText(List<String> likeText) {
+        setLikeText(likeText.toArray(Strings.EMPTY_ARRAY));
+    }
+
     public String[] getMoreLikeFields() {
         return moreLikeFields;
     }

src/main/java/org/elasticsearch/index/query/MoreLikeThisQueryParser.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.index.query;
 
 import com.google.common.collect.Lists;
+import com.google.common.collect.ObjectArrays;
 import com.google.common.collect.Sets;
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.queries.TermsFilter;
@@ -207,9 +208,11 @@ public Query parse(QueryParseContext parseContext) throws IOException, QueryPars
             }
             // fetching the items with multi-get
             List<LikeText> likeTexts = fetchService.fetch(items);
+            // collapse the text onto the same field name
+            Collection<LikeText> likeTextsCollapsed = collapseTextOnField(likeTexts);
             // right now we are just building a boolean query
             BooleanQuery boolQuery = new BooleanQuery();
-            for (LikeText likeText : likeTexts) {
+            for (LikeText likeText : likeTextsCollapsed) {
                 addMoreLikeThis(boolQuery, mltQuery, likeText);
             }
             // exclude the items from the search
@@ -260,6 +263,19 @@ private List<String> removeUnsupportedFields(List<String> moreLikeFields, Analyz
         return moreLikeFields;
     }
 
+    public static Collection<LikeText> collapseTextOnField (Collection<LikeText> likeTexts) {
+        Map<String, LikeText> collapsedTexts = new HashMap<>();
+        for (LikeText likeText : likeTexts) {
+            String field = likeText.field;
+            String[] text = likeText.text;
+            if (collapsedTexts.containsKey(field)) {
+                text = ObjectArrays.concat(collapsedTexts.get(field).text, text, String.class);
+            }
+            collapsedTexts.put(field, new LikeText(field, text));
+        }
+        return collapsedTexts.values();
+    }
+
     private void removeUnsupportedFields(MultiGetRequest.Item item, Analyzer analyzer, boolean failOnUnsupportedField) throws IOException {
         item.fields((String[]) removeUnsupportedFields(Arrays.asList(item.fields()), analyzer, failOnUnsupportedField).toArray());
     }

src/test/java/org/elasticsearch/index/query/SimpleIndexQueryParserTests.java

@@ -33,6 +33,7 @@
 import org.elasticsearch.action.get.MultiGetRequest;
 import org.elasticsearch.cache.recycler.CacheRecyclerModule;
 import org.elasticsearch.cluster.ClusterService;
+import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.bytes.BytesArray;
 import org.elasticsearch.common.compress.CompressedString;
 import org.elasticsearch.common.inject.AbstractModule;
@@ -65,6 +66,7 @@
 import org.elasticsearch.index.search.geo.GeoPolygonFilter;
 import org.elasticsearch.index.search.geo.InMemoryGeoBoundingBoxFilter;
 import org.elasticsearch.index.search.morelikethis.MoreLikeThisFetchService;
+import org.elasticsearch.index.search.morelikethis.MoreLikeThisFetchService.LikeText;
 import org.elasticsearch.index.settings.IndexSettingsModule;
 import org.elasticsearch.index.similarity.SimilarityModule;
 import org.elasticsearch.indices.fielddata.breaker.CircuitBreakerService;
@@ -1680,16 +1682,11 @@ public void testMoreLikeThisIds() throws Exception {
         MoreLikeThisQueryParser parser = (MoreLikeThisQueryParser) queryParser.queryParser("more_like_this");
         parser.setFetchService(new MockMoreLikeThisFetchService());
 
-        List<MoreLikeThisFetchService.LikeText> likeTexts = new ArrayList<>();
-        String index = "test";
-        String type = "person";
-        for (int i = 1; i < 5; i++) {
-            for (String field : new String[]{"name.first", "name.last"}) {
-                MoreLikeThisFetchService.LikeText likeText = new MoreLikeThisFetchService.LikeText(
-                        field, index + " " + type + " " + i + " " + field);
-                likeTexts.add(likeText);
-            }
-        }
+        List<LikeText> likeTexts = new ArrayList<>();
+        likeTexts.add(new LikeText("name.first", new String[]{
+                "test person 1 name.first", "test person 2 name.first", "test person 3 name.first", "test person 4 name.first"}));
+        likeTexts.add(new LikeText("name.last", new String[]{
+                "test person 1 name.last", "test person 2 name.last", "test person 3 name.last", "test person 4 name.last"}));
 
         IndexQueryParserService queryParser = queryParser();
         String query = copyToStringFromClasspath("/org/elasticsearch/index/query/mlt-ids.json");
@@ -1700,7 +1697,7 @@ public void testMoreLikeThisIds() throws Exception {
 
         // check each clause is for each item
         BooleanClause[] boolClauses = booleanQuery.getClauses();
-        for (int i=0; i<likeTexts.size(); i++) {
+        for (int i = 0; i < likeTexts.size(); i++) {
             BooleanClause booleanClause = booleanQuery.getClauses()[i];
             assertThat(booleanClause.getOccur(), is(BooleanClause.Occur.SHOULD));
             assertThat(booleanClause.getQuery(), instanceOf(MoreLikeThisQuery.class));