.. _es-guide-reference-mapping-id-field:

========
Id Field
========

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 the **ids** query/filter.


The **_id** field can be enabled to be indexed, and possibly stored, using:


.. code-block:: js


    {
        "tweet" : {
            :ref:`_id" : {"index <es-guide-reference-mapping>`  ex <es-guide-reference-mapping>`  "not_analyzed", "store" : "yes"}
        }
    }


In order to maintain backward compatibility, a node level setting **index.mapping._id.indexed** can be set to **true** to make sure that the id is indexed when upgrading to **0.16**, though its recommended to not index the id.