[[painless-update-context]]
=== Update context

Use a Painless script in an {ref}/docs-update.html[update] operation to
add, modify, or delete fields within a single document.

*Variables*

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

`ctx['op']` (`String`)::
        The name of the operation.

{ref}/mapping-routing-field.html[`ctx['_routing']`] (`String`, read-only)::
        The value used to select a shard for document storage.

{ref}/mapping-index-field.html[`ctx['_index']`] (`String`, read-only)::
        The name of the index.

{ref}/mapping-type-field.html[`ctx['_type']`] (`String`, read-only)::
        The type of document within an index.

{ref}/mapping-id-field.html[`ctx['_id']`] (`int`, read-only)::
        The unique document id.

`ctx['_version']` (`int`, read-only)::
        The current version of the document.

`ctx['_now']` (`long`, read-only)::
        The current timestamp in milliseconds.

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

*Side Effects*

`ctx['op']`::
        Use the default of `index` to update a document. Set to `none` to
        specify no operation or `delete` to delete the current document from
        the index.

{ref}/mapping-source-field.html[`ctx['_source']`]::
        Modify the values in the `Map/List` structure to add, modify, or delete
        the fields of a document.

*Return*

`void`::
        No expected return value.

*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>>.

The following query updates a document to be sold, and sets the cost
to the actual price paid after discounts:

[source,console]
--------------------------------------------------
POST /seats/_update/3
{
    "script": {
        "source": "ctx._source.sold = true; ctx._source.cost = params.sold_cost",
        "lang": "painless",
        "params": {
            "sold_cost": 26
        }
    }
}
--------------------------------------------------
// TEST[setup:seats]