==== Metadata: Document Identity
There are four metadata fields ((("metadata, document", "identity")))associated with document identity:
_id::
The string ID of the document
_type::
The type name of the document
_index::
The index where the document lives
_uid::
The _type and _id concatenated together as type#id
By default, the _uid field is((("id field"))) stored (can be retrieved) and
indexed (searchable). The _type field((("type field")))((("index field")))((("uid field"))) is indexed but not stored,
and the _id and _index fields are neither indexed nor stored, meaning
they don't really exist.
In spite of this, you can query the _id field as though it were a real
field. Elasticsearch uses the _uid field to derive the _id. Although you
can change the index and store settings for these fields, you almost
never need to do so.
The _id field does have one setting that you may want to use: the path
setting tells((("id field", "path setting")))((("path setting, id field"))) Elasticsearch that it should extract the value for the
_id from a field within the document itself.
PUT /my_index { "mappings": { "my_type": { "_id": { "path": "doc_id" <1> }, "properties": { "doc_id": { "type": "string", "index": "not_analyzed" } } } }
// SENSE: 070_Index_Mgmt/33_ID_path.json
<1> Extract the doc _id from the doc_id field.
Then, when you index a document:
POST /my_index/my_type { "doc_id": "123"
// SENSE: 070_Index_Mgmt/33_ID_path.json
the _id value will be ((("doc_id field")))extracted from the doc_id field in the document
body:
{ "_index": "my_index", "_type": "my_type", "_id": "123", <1> "_version": 1, "created": true
<1> The _id has been extracted correctly.
WARNING: While this is very convenient, be aware that it has a slight
performance impact on bulk requests (see <