[[mapping-index-field]]
=== `_index` field

The name of the index that contains the document.  This field is not indexed
but can be automatically derived from the index itself.

Its value is accessible in queries, aggregations, scripts, and when sorting:

[source,js]
--------------------------
# Example documents
PUT index_1/my_type/1
{
  "text": "Document in index 1"
}

PUT index_2/my_type/2
{
  "text": "Document in index 2"
}

GET index_1,index_2/_search
{
  "query": {
    "terms": {
      "_index": ["index_1", "index_2"] <1>
    }
  },
  "aggs": {
    "indices": {
      "terms": {
        "field": "_index", <2>
        "size": 10
      }
    }
  },
  "sort": [
    {
      "_index": { <3>
        "order": "asc"
      }
    }
  ],
  "script_fields": {
    "index_name": {
      "script": "doc['_index']" <4>
    }
  }
}
--------------------------
// AUTOSENSE

<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 (inline scripts must be <<enable-dynamic-scripting,enabled>> for this example to work)
