Access fields in a document with the field API
Access fields in a document with the field
API
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 #78920.
Use the field
API to access document fields:
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:
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
.
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
.
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:
$(‘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 For example, the following script uses the outdated syntax to determine the difference in milliseconds between two complex datetime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:
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:
ZonedDateTime start = field('start').get(null);
ZonedDateTime end = field('end').get(null);
return start == null || end == null ? -1 : ChronoUnit.MILLIS.between(start, end)
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).
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 #79105.
Mapped field type | Returned type from field | Returned type from doc | ||
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