OpenSearch/docs/painless/painless-contexts/painless-field-context.asciidoc

[[painless-field-context]]
=== Field context

Use a Painless script to create a
{ref}/search-fields.html#script-fields[script field] to return
a customized value for each document in the results of a query.

*Variables*

`params` (`Map`, read-only)::
        User-defined parameters passed in as part of the query.

`doc` (`Map`, read-only)::
        Contains the fields of the specified document where each field is a
        `List` of values.

{ref}/mapping-source-field.html[`params['_source']`] (`Map`, read-only)::
        Contains extracted JSON in a `Map` and `List` structure for the fields
        existing in a stored document.

*Return*

`Object`::
        The customized value for each document.

*API*

The standard <<painless-api-reference, Painless API>> is available.


*Example*

To run this example, first follow the steps in
<<painless-context-examples, context examples>>.

You can then use these two example scripts to compute custom information
for each search hit and output it to two new fields.

The first script gets the doc value for the `datetime` field and calls
the `getDayOfWeek` function to determine the corresponding day of the week.

[source,Painless]
----
doc['datetime'].value.getDayOfWeek();
----

The second script calculates the number of actors. Actors' names are stored
as a text array in the `actors` field.

[source,Painless]
----
params['_source']['actors'].length;                        <1>
----

<1> By default, doc values are not available for text fields. However,
    you can still calculate the number of actors by extracting actors
    from `_source`. Note that `params['_source']['actors']` is a list.


Submit the following request:

[source,console]
----
GET seats/_search
{
  "query": {
    "match_all": {}
  },
  "script_fields": {
    "day-of-week": {
      "script": {
        "source": "doc['datetime'].value.getDayOfWeek()"
      }
    },
    "number-of-actors": {
      "script": {
        "source": "params['_source']['actors'].length"
      }
    }
  }
}
----
// TEST[skip: requires setup from other pages]