_id field

Each document has an _id that uniquely identifies it, which is indexed so that documents can be looked up either with the GET API or the ids query. The _id can either be assigned at indexing time, or a unique _id can be generated by Elasticsearch. This field is not configurable in the mappings.

The value of the _id field is accessible in queries such as term, terms, match, and query_string.

				
					# Example documents
				PUT my-index-000001/_doc/1
					{
  "text": "Document with ID 1"
}
				PUT my-index-000001/_doc/2?refresh=true
					{
  "text": "Document with ID 2"
}
				GET my-index-000001/_search
					{
  "query": {
    "terms": {
      "_id": [ "1", "2" ]
    }
  }
}
		

1. Querying on the _id field (also see the ids query)

The _id field is restricted from use in aggregations, sorting, and scripting. In case sorting or aggregating on the _id field is required, it is advised to duplicate the content of the _id field into another field that has doc_values enabled.