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_index field

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_index field

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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:

response = client.index(
  index: 'index_1',
  id: 1,
  body: {
    text: 'Document in index 1'
  }
)
puts response

response = client.index(
  index: 'index_2',
  id: 2,
  refresh: true,
  body: {
    text: 'Document in index 2'
  }
)
puts response

response = client.search(
  index: 'index_1,index_2',
  body: {
    query: {
      terms: {
        _index: [
          'index_1',
          'index_2'
        ]
      }
    },
    aggregations: {
      indices: {
        terms: {
          field: '_index',
          size: 10
        }
      }
    },
    sort: [
      {
        _index: {
          order: 'asc'
        }
      }
    ],
    script_fields: {
      index_name: {
        script: {
          lang: 'painless',
          source: "doc['_index']"
        }
      }
    }
  }
)
puts response
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']" 
      }
    }
  }
}

Querying on the _index field

Aggregating on the _index field

Sorting on the _index field

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.

When specifying a remote index name such as cluster_1:index_3, the query must contain the separator character :. For example, a wildcard query on cluster_*:index_3 would match documents from the remote index. However, a query on cluster*index_1 is only matched against local indices, since no separator is present. This behavior aligns with the usual resolution rules for remote index names.

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