Retrieving specific fields using the Elasticsearch Java API

Question

I am using the Java API for Elasticsearch. Having saved entities into indexes, it is possible to retrieve them together with the complete source. However, I only want to retrieve selected fields, and that is not working.

The folowing sample code:

SearchResponse response = client.prepareSearch("my-index")
   .setTypes("my-type")
   .setSearchType(SearchType.QUERY_AND_FETCH)
   .setFetchSource(true)
   .setQuery(QueryBuilders.termsQuery("field1", "1234"))
   .addFields("field1")
   .execute()
   .actionGet();

for (SearchHit hit : response.getHits()){
   Map<String, SearchHitField> fields = hit.getFields();
   System.out.println(fields.size());
   Map map = hit.getSource();
   map.toString();
}

will retrieve the correct entities from the index, including the complete source.

For example, this is a snippet of the response :

"hits" : {
  "total" : 1301,
  "max_score" : 0.99614644,
  "hits" : [ {
  "_index" : "my-index",
  "_type" : "my-type",
  "_id" : "AU2P68COpzIypBTd80np",
  "_score" : 0.99614644,
  "_source":{"field1":"1234", ...}]}
}, {

However, while response.getHits() returns the expected number of hits, the fields and source within each hit is empty.

I am expecting each hit to contain the field specified in the line:

.addFields("field1")

Commenting out the line

.setFetchSource(true)

will cause the response not to include the source at all.

The version of Elasticsearch is 1.5.0

The following is the maven dependency the Java API:

<dependency>
   <groupId>com.sksamuel.elastic4s</groupId>
   <artifactId>elastic4s_2.11</artifactId>
   <version>1.5.5</version>
</dependency>

Obiously, for performance reasons, I don't want to have to retrieve the complete entity. Does anyone know how to limit the retrieval to selected fields? Thanks

Answer 1

You can specify the fields you need using the setFetchSource(String[] includes, String[] excludes) method. Try this instead

SearchResponse response = client.prepareSearch("my-index")
   .setTypes("my-type")
   .setSearchType(SearchType.QUERY_AND_FETCH)
   .setFetchSource(new String[]{"field1"}, null)
   .setQuery(QueryBuilders.termsQuery("field1", "1234"))
   .execute()
   .actionGet();

for (SearchHit hit : response.getHits()){
   Map map = hit.getSource();
   map.toString();
}

map will only contain the fields you've specified.

Note that .setFetchSource("field1", null) (if you need a single field) or .setFetchSource("field*", null) (if you need several wildcarded fields) would work, too.