elasticsearch/docs/reference/mapping/fields/id-field.asciidoc

[[mapping-id-field]]
=== `_id`

Each document indexed is associated with an id and a type. The `_id`
field can be used to index just the id, and possible also store it. By
default it is not indexed and not stored (thus, not created).

Note, even though the `_id` is not indexed, all the APIs still work
(since they work with the `_uid` field), as well as fetching by ids
using `term`, `terms` or `prefix` queries/filters (including the
specific `ids` query/filter).

The `_id` field can be enabled to be indexed, and possibly stored,
using the appropriate mapping attributes:

[source,js]
--------------------------------------------------
{
    "tweet" : {
        "_id" : {
            "index" : "not_analyzed",
            "store" : true
        }
    }
}
--------------------------------------------------