elasticsearch/docs/reference/scripting/access-fields.asciidoc

[[script-fields-api]]
== Access fields in a document with the `field` API
++++
<titleabbrev>Access fields in a document</titleabbrev>
++++

beta::["The `field` API is still in development and should be considered a beta feature. The API is subject to change and this iteration is likely not the final state. For feature status, refer to {es-issue}78920[#78920]."]

Use the `field` API to access document fields:

[source,painless]
----
field('my_field').get(<default_value>)
----

This API fundamentally changes how you access documents in Painless. Previously,
you had to access the `doc` map with the field name that you wanted to access:

[source,painless]
----
doc['my_field'].value
----

Accessing document fields this way didn't handle missing values or missing
mappings, which meant that to write robust Painless scripts, you needed to
include logic to check that both fields and values exist.

Instead, use the `field` API, which is the preferred approach to access
documents in Painless. The `field` API handles missing values, and will evolve
to abstract access to `_source` and `doc_values`.

NOTE: Some fields aren't yet compatible with the `fields` API, such as `text` or
`geo` fields. Continue using `doc` to access field types that the `field` API
doesn't support.

The `field` API returns a `Field` object that iterates over fields with 
multiple values, providing access to the underlying value through the
`get(<default_value>)` method, as well as type conversion and helper methods. 

The `field` API returns the default value that you specify, regardless of
whether the field exists or has any values for the current document.
This means that the `field` API can handle missing values without requiring 
additional logic. For a reference type such as `keyword`, the default 
value can be `null`. For a primitive type such as `boolean` or `long`, the
default value must be a matching primitive type, such as `false` or `1`. 

[discrete]
=== Convenient, simpler access
Instead of explicitly calling the `field` API with the `get()` method, you can
include the `$` shortcut. Just include the `$` symbol, field name, and a default
value, in case the field doesn't have a value:

[source,painless]
----
$(‘field’, <default_value>)
----

With these enhanced capabilities and simplified syntax, you can write scripts
that are shorter, less complex, and easier to read. For example, the following
script uses the outdated syntax to determine the difference in milliseconds
between two complex `datetime` values from an indexed document:

[source,painless]
----
if (doc.containsKey('start') && doc.containsKey('end')) {
   if (doc['start'].size() > 0 && doc['end'].size() > 0) {
       ZonedDateTime start = doc['start'].value;
       ZonedDateTime end = doc['end'].value;
       return ChronoUnit.MILLIS.between(start, end);
   } else {
       return -1;
   }
} else {
   return -1;
}
----

Using the `field` API, you can write this same script much more succinctly,
without requiring additional logic to determine whether fields exist before
operating on them:

[source,painless]
----
ZonedDateTime start = field('start').get(null);
ZonedDateTime end = field('end').get(null);
return start == null || end == null ? -1 : ChronoUnit.MILLIS.between(start, end)
----

[discrete]
=== Supported mapped field types
The following table indicates the mapped field types that the `field` API
supports. For each supported type, values are listed that are returned by the
`field` API (from the `get` and `as<Type>` methods) and the `doc` map (from the
`getValue` and `get` methods). 

NOTE: The `fields` API currently doesn't support some fields, but you can still
access those fields through the `doc` map. For the most current list of
supported fields, refer to {es-issue}79105[#79105].

[cols="1,1,1,1,1",options="header",]
|========
|Mapped field type
2+|Returned type from `field`
2+|Returned type from `doc`
h|              h|`get`      h|`as<Type>`    h|`getValue` h|`get`
 |`binary`        |`ByteBuffer` |-             |`BytesRef`  |`BytesRef`
 |`boolean`       |`boolean`    |-             |`boolean`   |`Boolean`
 |`keyword`       |`String`     |-             |`String`    |`String`
 |`long`          |`long`       |-             |`long`      |`Long`
 |`integer`       |`int`        |-             |`long`      |`Long`
 |`short`         |`short`      |-             |`long`      |`Long`
 |`byte`          |`byte`       |-             |`long`      |`Long`
 |`double`        |`double`     |-             |`double`    |`Double`
 |`scaled_float`  |`double`     |-             |`double`    |`Double`
 |`half_float`    |`float`      |-             |`double`    |`Double`
 |`unsigned_long` |`long`       |`BigInteger`  |`long`      |`Long`
 |`date`          |`ZonedDateTime` |-          |`ZonedDateTime` |`ZonedDateTime`
 |`date_nanos`    |`ZonedDateTime` |-          |`ZonedDateTime` |`ZonedDateTime`
 |`ip`            |`IpAddress`     |`String`  |`String`    |`String`
 |`_version`      |`long`       |-             |`long`      |`Long`
 |`_seq_no`       |`long`       |-             |`long`      |`Long`
 |`version`       |`Version`    |`String`      |`String`    |`String`
 |`murmur3`       |`long`       |-             |`long`      |`Long`
 |`constant_keyword` |`String`  |-             |`String`    |`String`
 |`wildcard`      |`String`     |-             |`String`    |`String`
 |`flattened`     |`String`     |-             |`String`    |`String`
|========