How to do a "join"/"sub-query" using ElasticSearch?

Question

I'm new to ElasticSearch, and I would like to able to do a query against an index, which then uses a part of the result to do another query.

For example, we have a tags index which we can query for a matching tag. That index contains stored fields identifying the content it's associated with (hooked to). Each type of content has it's own index. I need to be able to query for a tag match, and have it return not only the tag result, but a stored field (in this case title) from the content which it is associated with (different index).

Answer 1

I faced with the similar problem. You need a join here. Elasticsearch Team advises to use application side. ES emulates a relational database by implementing joins in our application: http://www.elasticsearch.org/guide/en/elasticsearch/guide/current/application-joins.html So you can use any of the ES client and write something similar

    SearchResponse response = client.prepareSearch(scriptVersionFirst)
                   .setTypes("yourtype")
                   .setQuery(QueryBuilders.termQuery("multi", "test"))
                   .setFrom(0).setSize(60).setExplain(true)
                   .execute()
                   .actionGet();

    if (response != null) {
        SearchHits hitList = response.getHits();
        if (hitList != null) {
            SearchHit[] hits = hitList.hits();          
            for (SearchHit hit : hits) 
                MethodPojo source = gson.fromJson(hit.getSourceAsString(), MethodPojo.class);
                System.out.println("Found: " + getMethodResultEntity(scriptVersionSecond, hit.getType(), source.getMethodName(), source.getMethodDesc(), source.getRequest()));
            }
        }

Here function getMethodResultEntity return result of other get query.

P.S. Im using here ES java client. It's a little bit heavy. If you need java client it's better to use jest client - much light version for simple situation.