OpenSearch/docs/reference/search/search-fields.asciidoc

[discrete]
[[search-fields]]
=== Retrieve selected fields

By default, each hit in the search response includes the document
<<mapping-source-field,`_source`>>, which is the entire JSON object that was
provided when indexing the document. If you only need certain source fields in
the search response, you can use the <<source-filtering,source filtering>> to
restrict what parts of the source are returned.

Returning fields using only the document source has some limitations:

* The `_source` field does not include <<multi-fields, multi-fields>> or
<<alias, field aliases>>. Likewise, a field in the source does not contain
values copied using the <<copy-to,`copy_to`>> mapping parameter.
* Since the `_source` is stored as a single field in Lucene, the whole source
object must be loaded and parsed, even if only a small number of fields are
needed.

To avoid these limitations, you can:

* Use the <<docvalue-fields, `docvalue_fields`>>
parameter to get values for selected fields. This can be a good
choice when returning a fairly small number of fields that support doc values,
such as keywords and dates.
* Use the <<request-body-search-stored-fields, `stored_fields`>> parameter to get the values for specific  stored fields. (Fields that use the <<mapping-store,`store`>> mapping option.)

You can find more detailed information on each of these methods in the 
following sections:

* <<source-filtering>>
* <<docvalue-fields>>
* <<stored-fields>>

[discrete]
[[source-filtering]]
=== Source filtering

You can use the `_source` parameter to select what fields of the source are
returned. This is called _source filtering_.

The following search API request sets the `_source` request body parameter to
`false`. The document source is not included in the response.

[source,console]
----
GET /_search
{
  "_source": false,
  "query": {
    "match": {
      "user.id": "kimchy"
    }
  }
}
----

To return only a subset of source fields, specify a wildcard (`*`) pattern in
the `_source` parameter. The following search API request returns the source for
only the `obj` field and its properties.

[source,console]
----
GET /_search
{
  "_source": "obj.*",
  "query": {
    "match": {
      "user.id": "kimchy"
    }
  }
}
----

You can also specify an array of wildcard patterns in the `_source` field. The
following search API request returns the source for only the `obj1` and
`obj2` fields and their properties.

[source,console]
----
GET /_search
{
  "_source": [ "obj1.*", "obj2.*" ],
  "query": {
    "match": {
      "user.id": "kimchy"
    }
  }
}
----

For finer control, you can specify an object containing arrays of `includes` and
`excludes` patterns in the `_source` parameter.

If the `includes` property is specified, only source fields that match one of
its patterns are returned. You can exclude fields from this subset using the
`excludes` property.

If the `includes` property is not specified, the entire document source is
returned, excluding any fields that match a pattern in the `excludes` property.

The following search API request returns the source for only the `obj1` and
`obj2` fields and their properties, excluding any child `description` fields.

[source,console]
----
GET /_search
{
  "_source": {
    "includes": [ "obj1.*", "obj2.*" ],
    "excludes": [ "*.description" ]
  },
  "query": {
    "term": {
      "user.id": "kimchy"
    }
  }
}
----


[discrete]
[[docvalue-fields]]
=== Doc value fields

You can use the <<docvalue-fields,`docvalue_fields`>> parameter to return
<<doc-values,doc values>> for one or more fields in the search response.

Doc values store the same values as the `_source` but in an on-disk,
column-based structure that's optimized for sorting and aggregations. Since each
field is stored separately, {es} only reads the field values that were requested
and can avoid loading the whole document `_source`.

Doc values are stored for supported fields by default. However, doc values are
not supported for <<text,`text`>> or
{plugins}/mapper-annotated-text-usage.html[`text_annotated`] fields.

The following search request uses the `docvalue_fields` parameter to
retrieve doc values for the following fields:

* Fields with names starting with `my_ip`
* `my_keyword_field`
* Fields with names ending with `_date_field`

[source,console]
----
GET /_search
{
  "query": {
    "match_all": {}
  },
  "docvalue_fields": [
    "my_ip*",                     <1>
    {
      "field": "my_keyword_field" <2>
    },
    {
      "field": "*_date_field",
      "format": "epoch_millis"    <3>
    }
  ]
}
----

<1> Wildcard patten used to match field names, specified as a string.
<2> Wildcard patten used to match field names, specified as an object.
<3> With the object notation, you can use the `format` parameter to specify a
    format for the field's returned doc values. <<date,Date fields>> support a
    <<mapping-date-format,date `format`>>. <<number,Numeric fields>> support a
    https://docs.oracle.com/javase/8/docs/api/java/text/DecimalFormat.html[DecimalFormat
    pattern]. Other field data types do not support the `format` parameter.

TIP: You cannot use the `docvalue_fields` parameter to retrieve doc values for
nested objects. If you specify a nested object, the search returns an empty
array (`[ ]`) for the field. To access nested fields, use the
<<request-body-search-inner-hits, `inner_hits`>> parameter's `docvalue_fields`
property.


[discrete]
[[stored-fields]]
=== Stored fields

It's also possible to store an individual field's values by using the
<<mapping-store,`store`>> mapping option. You can use the
<<request-body-search-stored-fields, `stored_fields`>> parameter to include
these stored values in the search response.