Elasticsearch: Java API allows to create invalid queries by adding a top_hits aggregation without fields

TopHitsAggWithoutFieldsTest.java

package sandbox;

import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.index.query.QueryBuilders;
import org.elasticsearch.search.aggregations.AggregationBuilders;
import org.elasticsearch.test.ElasticsearchIntegrationTest;
import org.junit.Before;
import org.junit.Test;

/**
 * Created by hkorte on 2015-04-07.
 * <p>
 *   This test is failing, because a SearchPhaseExecutionException is thrown
 *   in line 47 for a top_hits aggregation without fields defined like that:
 *   <code>AggregationBuilders.topHits("topHitsAgg").setNoFields()</code>
 * </p>
 * <p>
 *   IMHO this is misleading. I see two options to avoid this confusion:
 *   <ul>
 *       <li>the top_hits API allows setting "fields" to an empty array</li>
 *       <li>the Java API does not offer this method</li>
 *   </ul>
 * </p>
 */
@ElasticsearchIntegrationTest.ClusterScope(scope = ElasticsearchIntegrationTest.Scope.SUITE)
public class TopHitsAggWithoutFieldsTest extends ElasticsearchIntegrationTest {

    @Override
    @Before
    public void setUp() throws Exception {
        super.setUp();
        createIndex("test");
        ensureGreen("test");
    }

    @Test
    public void testTopHitsAggWithoutFields() throws Exception {
        SearchResponse sr;

        sr = client().prepareSearch().setQuery(QueryBuilders.matchAllQuery())
                .addAggregation(AggregationBuilders.topHits("topHitsAgg").setSize(1)).get();

        sr = client().prepareSearch().setQuery(QueryBuilders.matchAllQuery())
                .addAggregation(AggregationBuilders.topHits("topHitsAgg").setFetchSource("", "*").setSize(1)).get();

        sr = client().prepareSearch().setQuery(QueryBuilders.matchAllQuery())
                .addAggregation(AggregationBuilders.topHits("topHitsAgg").setNoFields().setSize(1)).get();
    }
}