[[search-fields]]
== Retrieve selected fields from a search
++++
<titleabbrev>Retrieve selected fields</titleabbrev>
++++

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. There are two recommended methods to
retrieve selected fields from a search query:

* Use the <<search-fields-param,`fields` option>> to extract the values of
fields present in the index mapping
* Use the <<source-filtering,`_source` option>> if you need to access the original data that was passed at index time

You can use both of these methods, though the `fields` option is preferred
because it consults both the document data and index mappings. In some
instances, you might want to use <<field-retrieval-methods,other methods>> of
retrieving data.

[discrete]
[[search-fields-param]]
=== The `fields` option
To retrieve specific fields in the search response, use the `fields` parameter.
// tag::fields-param-desc[]
Because it consults the index mappings, the `fields` parameter provides several
advantages over referencing the `_source` directly. Specifically, the `fields`
parameter:

* Returns each value in a standardized way that matches its mapping type
* Accepts <<multi-fields,multi-fields>> and <<field-alias,field aliases>>
* Formats dates and spatial data types
* Retrieves <<runtime-retrieving-fields,runtime field values>>
* Returns fields calculated by a script at index time
// end::fields-param-desc[]

Other mapping options are also respected, including
<<ignore-above,`ignore_above`>>, <<ignore-malformed,`ignore_malformed`>>, and
<<null-value,`null_value`>>.

The `fields` option returns values in the way that matches how {es} indexes
them. For standard fields, this means that the `fields` option looks in
`_source` to find the values, then parses and formats them using the mappings.

[discrete]
[[search-fields-request]]
==== Search for specific fields
The following search request uses the `fields` parameter to retrieve values
for the `user.id` field, all fields starting with `http.response.`, and the
`@timestamp` field.

Using object notation, you can pass a `format` parameter for certain fields to
apply a custom format for the field's values:

* <<date,`date`>> and <<date_nanos,`date_nanos`>> fields accept a <<mapping-date-format,date format>>
* <<spatial_datatypes, Spatial fields>> accept either `geojson` for http://www.geojson.org[GeoJSON] (the default) or `wkt` for
{wikipedia}/Well-known_text_representation_of_geometry[Well Known Text]

Other field types do not support the `format` parameter.

[source,console]
----
POST my-index-000001/_search
{
  "query": {
    "match": {
      "user.id": "kimchy"
    }
  },
  "fields": [
    "user.id",
    "http.response.*",         <1>
    {
      "field": "@timestamp",
      "format": "epoch_millis" <2>
    }
  ],
  "_source": false
}
----
// TEST[setup:my_index]
// TEST[s/_search/_search\?filter_path=hits/]

// tag::fields-param-callouts[]
<1> Both full field names and wildcard patterns are accepted.
<2> Use the `format` parameter to apply a custom format for the field's values.
// end::fields-param-callouts[]

[discrete]
[[search-fields-response]]
==== Response always returns an array

The `fields` response always returns an array of values for each field,
even when there is a single value in the `_source`. This is because {es} has
no dedicated array type, and any field could contain multiple values. The
`fields` parameter also does not guarantee that array values are returned in
a specific order. See the mapping documentation on <<array,arrays>> for more
background.

The response includes values as a flat list in the `fields` section for each
hit. Because the `fields` parameter doesn't fetch entire objects, only leaf
fields are returned.

[source,console-result]
----
{
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "my-index-000001",
        "_id" : "0",
        "_score" : 1.0,
        "_type" : "_doc",
        "fields" : {
          "user.id" : [
            "kimchy"
          ],
          "@timestamp" : [
            "4098435132000"
          ],
          "http.response.bytes": [
            1070000
          ],
          "http.response.status_code": [
            200
          ]
        }
      }
    ]
  }
}
----
// TESTRESPONSE[s/"max_score" : 1.0/"max_score" : $body.hits.max_score/]
// TESTRESPONSE[s/"_score" : 1.0/"_score" : $body.hits.hits.0._score/]

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

The `fields` response for <<nested,`nested` fields>> is slightly different from that
of regular object fields. While leaf values inside regular `object` fields are
returned as a flat list, values inside `nested` fields are grouped to maintain the
independence of each object inside the original nested array.
For each entry inside a nested field array, values are again returned as a flat list
unless there are other `nested` fields inside the parent nested object, in which case
the same procedure is repeated again for the deeper nested fields.

Given the following mapping where `user` is a nested field, after indexing
the following document and retrieving all fields under the `user` field:

[source,console]
--------------------------------------------------
PUT my-index-000001
{
  "mappings": {
    "properties": {
      "group" : { "type" : "keyword" },
      "user": {
        "type": "nested",
        "properties": {
          "first" : { "type" : "keyword" },
          "last" : { "type" : "keyword" }
        }
      }
    }
  }
}

PUT my-index-000001/_doc/1?refresh=true
{
  "group" : "fans",
  "user" : [
    {
      "first" : "John",
      "last" :  "Smith"
    },
    {
      "first" : "Alice",
      "last" :  "White"
    }
  ]
}

POST my-index-000001/_search
{
  "fields": ["*"],
  "_source": false
}
--------------------------------------------------

The response will group `first` and `last` name instead of
returning them as a flat list.

[source,console-result]
----
{
  "took": 2,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": {
      "value": 1,
      "relation": "eq"
    },
    "max_score": 1.0,
    "hits": [{
      "_index": "my-index-000001",
      "_id": "1",
      "_score": 1.0,
      "_type": "_doc",
      "fields": {
        "group" : ["fans"],
        "user": [{
            "first": ["John"],
            "last": ["Smith"],
          },
          {
            "first": ["Alice"],
            "last": ["White"],
          }
        ]
      }
    }]
  }
}
----
// TESTRESPONSE[s/"took": 2/"took": $body.took/]
// TESTRESPONSE[s/"max_score" : 1.0/"max_score" : $body.hits.max_score/]
// TESTRESPONSE[s/"_score" : 1.0/"_score" : $body.hits.hits.0._score/]

Nested fields will be grouped by their nested paths, no matter the pattern used
to retrieve them. For example, if you query only for the `user.first` field from
the previous example:

[source,console]
--------------------------------------------------
POST my-index-000001/_search
{
  "fields": ["user.first"],
  "_source": false
}
--------------------------------------------------
// TEST[continued]

The response returns only the user's first name, but still maintains the
structure of the nested `user` array:

[source,console-result]
----
{
  "took": 2,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": {
      "value": 1,
      "relation": "eq"
    },
    "max_score": 1.0,
    "hits": [{
      "_index": "my-index-000001",
      "_id": "1",
      "_score": 1.0,
      "_type": "_doc",
      "fields": {
        "user": [{
            "first": ["John"],
          },
          {
            "first": ["Alice"],
          }
        ]
      }
    }]
  }
}
----
// TESTRESPONSE[s/"took": 2/"took": $body.took/]
// TESTRESPONSE[s/"max_score" : 1.0/"max_score" : $body.hits.max_score/]
// TESTRESPONSE[s/"_score" : 1.0/"_score" : $body.hits.hits.0._score/]

However, when the `fields` pattern targets the nested `user` field directly, no
values will be returned because the pattern doesn't match any leaf fields.

[discrete]
[[retrieve-unmapped-fields]]
==== Retrieve unmapped fields
By default, the `fields` parameter returns only values of mapped fields.
However, {es} allows storing fields in `_source` that are unmapped, such as
setting <<dynamic-field-mapping,dynamic field mapping>> to `false` or by using
an object field with `enabled: false`. These options disable parsing and
indexing of the object content.

To retrieve unmapped fields in an object from `_source`, use the
`include_unmapped` option in the `fields` section:

[source,console]
----
PUT my-index-000001
{
  "mappings": {
    "enabled": false <1>
  }
}

PUT my-index-000001/_doc/1?refresh=true
{
  "user_id": "kimchy",
  "session_data": {
     "object": {
       "some_field": "some_value"
     }
   }
}

POST my-index-000001/_search
{
  "fields": [
    "user_id",
    {
      "field": "session_data.object.*",
      "include_unmapped" : true <2>
    }
  ],
  "_source": false
}
----

<1> Disable all mappings.
<2> Include unmapped fields matching this field pattern.

The response will contain field results under the  `session_data.object.*` path,
even if the fields are unmapped. The `user_id` field is also unmapped, but it
won't be included in the response because `include_unmapped` isn't set to
`true` for that field pattern.

[source,console-result]
----
{
  "took" : 2,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "my-index-000001",
        "_id" : "1",
        "_score" : 1.0,
        "_type" : "_doc",
        "fields" : {
          "session_data.object.some_field": [
            "some_value"
          ]
        }
      }
    ]
  }
}
----
// TESTRESPONSE[s/"took" : 2/"took": $body.took/]
// TESTRESPONSE[s/"max_score" : 1.0/"max_score" : $body.hits.max_score/]
// TESTRESPONSE[s/"_score" : 1.0/"_score" : $body.hits.hits.0._score/]

[discrete]
[[source-filtering]]
=== The `_source` option
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]
[[field-retrieval-methods]]
=== Other methods of retrieving data

.Using `fields` is typically better
****
These options are usually not required. Using the `fields` option is typically
the better choice, unless you absolutely need to force loading a stored or
`docvalue_fields`.
****

A document's `_source` is stored as a single field in Lucene. This structure
means that the whole `_source` object must be loaded and parsed even if you're
only requesting part of it. To avoid this limitation, you can try other options
for loading fields:

* 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).

{es} always attempts to load values from `_source`. This behavior has the same
implications of source filtering where {es} needs to load and parse the entire
`_source` to retrieve just one field.

[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 `user.id` field, all fields starting with `http.response.`, and the
`@timestamp` field:

[source,console]
----
GET my-index-000001/_search
{
  "query": {
    "match": {
      "user.id": "kimchy"
    }
  },
  "docvalue_fields": [
    "user.id",
    "http.response.*", <1>
    {
      "field": "date",
      "format": "epoch_millis" <2>
    }
  ]
}
----
// TEST[setup:my_index]

<1> Both full field names and wildcard patterns are accepted.
<2> Using object notation, you can pass a `format` parameter to apply a custom
    format for the field's 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 datatypes 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
<<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
`stored_fields` parameter to include these stored values in the search response.

WARNING: The `stored_fields` parameter is for fields that are explicitly marked as
stored in the mapping, which is off by default and generally not recommended.
Use <<source-filtering,source filtering>> instead to select
subsets of the original source document to be returned.

Allows to selectively load specific stored fields for each document represented
by a search hit.

[source,console]
--------------------------------------------------
GET /_search
{
  "stored_fields" : ["user", "postDate"],
  "query" : {
    "term" : { "user" : "kimchy" }
  }
}
--------------------------------------------------

`*` can be used to load all stored fields from the document.

An empty array will cause only the `_id` and `_type` for each hit to be
returned, for example:

[source,console]
--------------------------------------------------
GET /_search
{
  "stored_fields" : [],
  "query" : {
    "term" : { "user" : "kimchy" }
  }
}
--------------------------------------------------

If the requested fields are not stored (`store` mapping set to `false`), they will be ignored.

Stored field values fetched from the document itself are always returned as an array. On the contrary, metadata fields like `_routing` are never returned as an array.

Also only leaf fields can be returned via the `stored_fields` option. If an object field is specified, it will be ignored.

NOTE: On its own, `stored_fields` cannot be used to load fields in nested
objects -- if a field contains a nested object in its path, then no data will
be returned for that stored field. To access nested fields, `stored_fields`
must be used within an <<inner-hits, `inner_hits`>> block.

[discrete]
[[disable-stored-fields]]
===== Disable stored fields

To disable the stored fields (and metadata fields) entirely use: `_none_`:

[source,console]
--------------------------------------------------
GET /_search
{
  "stored_fields": "_none_",
  "query" : {
    "term" : { "user" : "kimchy" }
  }
}
--------------------------------------------------

NOTE: <<source-filtering,`_source`>> and <<request-body-search-version, `version`>> parameters cannot be activated if `_none_` is used.

[discrete]
[[script-fields]]
==== Script fields

You can use the `script_fields` parameter to retrieve a <<modules-scripting,script
evaluation>> (based on different fields) for each hit. For example:

[source,console]
--------------------------------------------------
GET /_search
{
  "query": {
    "match_all": {}
  },
  "script_fields": {
    "test1": {
      "script": {
        "lang": "painless",
        "source": "doc['price'].value * 2"
      }
    },
    "test2": {
      "script": {
        "lang": "painless",
        "source": "doc['price'].value * params.factor",
        "params": {
          "factor": 2.0
        }
      }
    }
  }
}
--------------------------------------------------
// TEST[setup:sales]

Script fields can work on fields that are not stored (`price` in
the above case), and allow to return custom values to be returned (the
evaluated value of the script).

Script fields can also access the actual `_source` document and
extract specific elements to be returned from it by using `params['_source']`.
Here is an example:

[source,console]
--------------------------------------------------
GET /_search
{
  "query": {
    "match_all": {}
  },
  "script_fields": {
    "test1": {
      "script": "params['_source']['message']"
    }
  }
}
--------------------------------------------------
// TEST[setup:my_index]

Note the `_source` keyword here to navigate the json-like model.

It's important to understand the difference between
`doc['my_field'].value` and `params['_source']['my_field']`. The first,
using the doc keyword, will cause the terms for that field to be loaded to
memory (cached), which will result in faster execution, but more memory
consumption. Also, the `doc[...]` notation only allows for simple valued
fields (you can't return a json object from it) and makes sense only for
non-analyzed or single term based fields. However, using `doc` is
still the recommended way to access values from the document, if at all
possible, because `_source` must be loaded and parsed every time it's used.
Using `_source` is very slow.
