Moved the check to fetch phase. This basically means that we throw

a better error message instead of an AOBE and not adding more restrictions.

Author: martijnvg

core/src/main/java/org/elasticsearch/index/query/NestedQueryBuilder.java

@@ -353,11 +353,6 @@ protected void doBuild(SearchContext parentSearchContext,
                 name, parentSearchContext, parentObjectMapper, nestedObjectMapper
             );
             setupInnerHitsContext(queryShardContext, nestedInnerHits);
-            if ((nestedInnerHits.hasFetchSourceContext() == false || nestedInnerHits.sourceRequested()) &&
-                nestedObjectMapper.parentObjectMapperAreNested(parentSearchContext.mapperService()) == false) {
-                throw new IllegalArgumentException("Cannot execute inner hits. One or more parent object fields of nested field [" +
-                    nestedObjectMapper.name() + "] are not nested. All parent fields need to be nested fields too");
-            }
             queryShardContext.nestedScope().previousLevel();
             innerHitsContext.addInnerHitDefinition(nestedInnerHits);
         }

core/src/main/java/org/elasticsearch/search/fetch/FetchPhase.java

@@ -263,18 +263,23 @@ private SearchHit createNestedSearchHit(SearchContext context, int nestedTopDocI
                 String nestedPath = nested.getField().string();
                 current.put(nestedPath, new HashMap<>());
                 Object extractedValue = XContentMapValues.extractValue(nestedPath, sourceAsMap);
-                List<Map<String, Object>> nestedParsedSource;
+                List<?> nestedParsedSource;
                 if (extractedValue instanceof List) {
                     // nested field has an array value in the _source
-                    nestedParsedSource = (List<Map<String, Object>>) extractedValue;
+                    nestedParsedSource = (List<?>) extractedValue;
                 } else if (extractedValue instanceof Map) {
                     // nested field has an object value in the _source. This just means the nested field has just one inner object,
                     // which is valid, but uncommon.
-                    nestedParsedSource = Collections.singletonList((Map<String, Object>) extractedValue);
+                    nestedParsedSource = Collections.singletonList(extractedValue);
                 } else {
                     throw new IllegalStateException("extracted source isn't an object or an array");
                 }
-                sourceAsMap = nestedParsedSource.get(nested.getOffset());
+                if ((nestedParsedSource.get(0) instanceof Map) == false &&
+                    nestedObjectMapper.parentObjectMapperAreNested(context.mapperService()) == false) {
+                    throw new IllegalArgumentException("Cannot execute inner hits. One or more parent object fields of nested field [" +
+                        nestedObjectMapper.name() + "] are not nested. All parent fields need to be nested fields too");
+                }
+                sourceAsMap = (Map<String, Object>) nestedParsedSource.get(nested.getOffset());
                 if (nested.getChild() == null) {
                     current.put(nestedPath, sourceAsMap);
                 } else {

core/src/test/java/org/elasticsearch/search/fetch/subphase/InnerHitsIT.java

@@ -402,45 +402,50 @@ public void testInnerHitsWithObjectFieldThatHasANestedField() throws Exception {
         List<IndexRequestBuilder> requests = new ArrayList<>();
         requests.add(client().prepareIndex("articles", "article", "1").setSource(jsonBuilder().startObject()
                 .field("title", "quick brown fox")
-                .startObject("comments")
-                .startArray("messages")
-                    .startObject().field("message", "fox eat quick").endObject()
-                    .startObject().field("message", "bear eat quick").endObject()
+                .startArray("comments")
+                    .startObject()
+                        .startArray("messages")
+                            .startObject().field("message", "fox eat quick").endObject()
+                            .startObject().field("message", "bear eat quick").endObject()
+                        .endArray()
+                    .endObject()
+                    .startObject()
+                        .startArray("messages")
+                            .startObject().field("message", "no fox").endObject()
+                        .endArray()
+                    .endObject()
                 .endArray()
-                .endObject()
                 .endObject()));
         indexRandom(true, requests);
 
-        SearchPhaseExecutionException e = expectThrows(
-            SearchPhaseExecutionException.class,
-            () -> client().prepareSearch("articles").setQuery(nestedQuery("comments.messages",
-                matchQuery("comments.messages.message", "fox"), ScoreMode.Avg).innerHit(new InnerHitBuilder())).get()
-        );
+        SearchResponse response = client().prepareSearch("articles").setQuery(nestedQuery("comments.messages",
+            matchQuery("comments.messages.message", "fox"), ScoreMode.Avg).innerHit(new InnerHitBuilder())).get();
         assertEquals("Cannot execute inner hits. One or more parent object fields of nested field [comments.messages] are " +
-            "not nested. All parent fields need to be nested fields too", e.shardFailures()[0].getCause().getMessage());
+            "not nested. All parent fields need to be nested fields too", response.getShardFailures()[0].getCause().getMessage());
 
-        e = expectThrows(
-            SearchPhaseExecutionException.class,
-            () -> client().prepareSearch("articles").setQuery(nestedQuery("comments.messages",
-                matchQuery("comments.messages.message", "fox"), ScoreMode.Avg).innerHit(new InnerHitBuilder()
-                .setFetchSourceContext(new FetchSourceContext(true)))).get()
-        );
+        response = client().prepareSearch("articles").setQuery(nestedQuery("comments.messages",
+            matchQuery("comments.messages.message", "fox"), ScoreMode.Avg).innerHit(new InnerHitBuilder()
+            .setFetchSourceContext(new FetchSourceContext(true)))).get();
         assertEquals("Cannot execute inner hits. One or more parent object fields of nested field [comments.messages] are " +
-            "not nested. All parent fields need to be nested fields too", e.shardFailures()[0].getCause().getMessage());
+            "not nested. All parent fields need to be nested fields too", response.getShardFailures()[0].getCause().getMessage());
 
-        SearchResponse response = client().prepareSearch("articles")
+        response = client().prepareSearch("articles")
                 .setQuery(nestedQuery("comments.messages", matchQuery("comments.messages.message", "fox"), ScoreMode.Avg)
                         .innerHit(new InnerHitBuilder().setFetchSourceContext(new FetchSourceContext(false)))).get();
         assertNoFailures(response);
         assertHitCount(response, 1);
         SearchHit hit = response.getHits().getAt(0);
         assertThat(hit.getId(), equalTo("1"));
         SearchHits messages = hit.getInnerHits().get("comments.messages");
-        assertThat(messages.getTotalHits(), equalTo(1L));
+        assertThat(messages.getTotalHits(), equalTo(2L));
         assertThat(messages.getAt(0).getId(), equalTo("1"));
         assertThat(messages.getAt(0).getNestedIdentity().getField().string(), equalTo("comments.messages"));
-        assertThat(messages.getAt(0).getNestedIdentity().getOffset(), equalTo(0));
+        assertThat(messages.getAt(0).getNestedIdentity().getOffset(), equalTo(2));
         assertThat(messages.getAt(0).getNestedIdentity().getChild(), nullValue());
+        assertThat(messages.getAt(1).getId(), equalTo("1"));
+        assertThat(messages.getAt(1).getNestedIdentity().getField().string(), equalTo("comments.messages"));
+        assertThat(messages.getAt(1).getNestedIdentity().getOffset(), equalTo(0));
+        assertThat(messages.getAt(1).getNestedIdentity().getChild(), nullValue());
 
         response = client().prepareSearch("articles")
                 .setQuery(nestedQuery("comments.messages", matchQuery("comments.messages.message", "bear"), ScoreMode.Avg)