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Joining queries

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Joining queries

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Performing full SQL-style joins in a distributed system like Elasticsearch is prohibitively expensive. Instead, Elasticsearch offers two forms of join which are designed to scale horizontally.

nested query: Documents may contains fields of type nested. These fields are used to index arrays of objects, where each object can be queried (with the nested query) as an independent document.
has_child and has_parent queries: A parent-child relationship can exist between two document types within a single index. The has_child query returns parent documents whose child documents match the specified query, while the has_parent query returns child documents whose parent document matches the specified query.

Nested Query

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See Nested Query

nestedQuery(
        "obj1",                                              
        boolQuery()                                          
                .must(matchQuery("obj1.name", "blue"))
                .must(rangeQuery("obj1.count").gt(5)),
        ScoreMode.Avg);

	path to nested document
	your query. Any fields referenced inside the query must use the complete path (fully qualified).
	score mode could be `ScoreMode.Max`, `ScoreMode.Min`, `ScoreMode.Total`, `ScoreMode.Avg` or `ScoreMode.None`

Has Child Query

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See Has Child Query

When using the has_child query it is important to use the PreBuiltTransportClient instead of the regular client:

Settings settings = Settings.builder().put("cluster.name", "elasticsearch").build();
TransportClient client = new PreBuiltTransportClient(settings);
client.addTransportAddress(new TransportAddress(new InetSocketAddress(InetAddresses.forString("127.0.0.1"), 9300)));

Otherwise the parent-join module doesn’t get loaded and the has_child query can’t be used from the transport client.

JoinQueryBuilders.hasChildQuery(
        "blog_tag",                                          
        termQuery("tag","something"),                        
        ScoreMode.None);

	child type to query against
	query
	score mode can be `ScoreMode.Avg`, `ScoreMode.Max`, `ScoreMode.Min`, `ScoreMode.None` or `ScoreMode.Total`

Has Parent Query

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See Has Parent

When using the has_parent query it is important to use the PreBuiltTransportClient instead of the regular client:

Settings settings = Settings.builder().put("cluster.name", "elasticsearch").build();
TransportClient client = new PreBuiltTransportClient(settings);
client.addTransportAddress(new TransportAddress(new InetSocketAddress(InetAddresses.forString("127.0.0.1"), 9300)));

Otherwise the parent-join module doesn’t get loaded and the has_parent query can’t be used from the transport client.

JoinQueryBuilders.hasParentQuery(
    "blog",                                                  
    termQuery("tag","something"),                            
    false);

	parent type to query against
	query
	whether the score from the parent hit should propagate to the child hit

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