_index field

When performing queries across multiple indexes, it is sometimes desirable to add query clauses that are associated with documents of only certain indexes. The _index field allows matching on the index a document was indexed into. Its value is accessible in certain queries and aggregations, and when sorting or scripting:

 PUT index_1/_doc/1 { "text": "Document in index 1" } PUT index_2/_doc/2?refresh=true { "text": "Document in index 2" } GET index_1,index_2/_search { "query": { "terms": { "_index": ["index_1", "index_2"] } }, "aggs": { "indices": { "terms": { "field": "_index", "size": 10 } } }, "sort": [ { "_index": { "order": "asc" } } ], "script_fields": { "index_name": { "script": { "lang": "painless", "source": "doc['_index']" } } } } 

1. Querying on the _index field
2. Aggregating on the _index field
3. Sorting on the _index field
4. Accessing the _index field in scripts

The _index field is exposed virtually — it is not added to the Lucene index as a real field. This means that you can use the _index field in a term or terms query (or any query that is rewritten to a term query, such as the match, query_string or simple_query_string query), as well as prefix and wildcard queries. However, it does not support regexp and fuzzy queries.

Queries on the _index field accept index aliases in addition to concrete index names.