From 8fd363789128ab4db93258d6eaf34e40b9197018 Mon Sep 17 00:00:00 2001
From: shaie <serera@gmail.com>
Date: Fri, 2 Dec 2016 09:14:45 +0200
Subject: [PATCH] Return correct term statistics when a field is not found in a
 shard (#21922)

If you ask for the term vectors of an artificial document with
term_statistics=true, but a shard does not have any terms of the doc's
field(s), it returns the doc's term vectors values as the shard-level
term statistics. This commit fixes that to return 0 for `ttf` and also
field-level aggregated statistics.

Closes #21906
---
 .../action/termvectors/TermVectorsWriter.java    | 16 +++++++++++++++-
 .../action/termvectors/GetTermVectorsIT.java     | 10 ++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/core/src/main/java/org/elasticsearch/action/termvectors/TermVectorsWriter.java b/core/src/main/java/org/elasticsearch/action/termvectors/TermVectorsWriter.java
index 6b5e497b8e5..06eea6367ed 100644
--- a/core/src/main/java/org/elasticsearch/action/termvectors/TermVectorsWriter.java
+++ b/core/src/main/java/org/elasticsearch/action/termvectors/TermVectorsWriter.java
@@ -71,7 +71,7 @@ final class TermVectorsWriter {
 
             // if no terms found, take the retrieved term vector fields for stats
             if (topLevelTerms == null) {
-                topLevelTerms = fieldTermVector;
+                topLevelTerms = EMPTY_TERMS;
             }
 
             TermsEnum topLevelIterator = topLevelTerms.iterator();
@@ -292,4 +292,18 @@ final class TermVectorsWriter {
         // further...
         output.writeVLong(Math.max(0, value + 1));
     }
+
+    /** Implements an empty {@link Terms}. */
+    private static final Terms EMPTY_TERMS = new Terms() {
+        @Override public TermsEnum iterator() throws IOException { return TermsEnum.EMPTY; }
+        @Override public long size() throws IOException { return 0; }
+        @Override public long getSumTotalTermFreq() throws IOException { return 0; }
+        @Override public long getSumDocFreq() throws IOException { return 0; }
+        @Override public int getDocCount() throws IOException { return 0; }
+        @Override public boolean hasFreqs() { return false; }
+        @Override public boolean hasOffsets() { return false; }
+        @Override public boolean hasPositions() { return false; }
+        @Override public boolean hasPayloads() { return false; }
+    };
+
 }
diff --git a/core/src/test/java/org/elasticsearch/action/termvectors/GetTermVectorsIT.java b/core/src/test/java/org/elasticsearch/action/termvectors/GetTermVectorsIT.java
index 3835edbbe9a..765e39b3fbf 100644
--- a/core/src/test/java/org/elasticsearch/action/termvectors/GetTermVectorsIT.java
+++ b/core/src/test/java/org/elasticsearch/action/termvectors/GetTermVectorsIT.java
@@ -848,6 +848,16 @@ public class GetTermVectorsIT extends AbstractTermVectorsTestCase {
                 .get();
         assertThat(resp.isExists(), equalTo(true));
         checkBrownFoxTermVector(resp.getFields(), "field1", false);
+
+        // Since the index is empty, all of artificial document's "term_statistics" should be 0/absent
+        Terms terms = resp.getFields().terms("field1");
+        assertEquals("sumDocFreq should be 0 for a non-existing field!", 0, terms.getSumDocFreq());
+        assertEquals("sumTotalTermFreq should be 0 for a non-existing field!", 0, terms.getSumTotalTermFreq());
+        TermsEnum termsEnum = terms.iterator(); // we're guaranteed to receive terms for that field
+        while (termsEnum.next() != null) {
+            String term = termsEnum.term().utf8ToString();
+            assertEquals("term [" + term + "] does not exist in the index; ttf should be 0!", 0, termsEnum.totalTermFreq());
+        }
     }
 
     public void testPerFieldAnalyzer() throws IOException {