[[painless-update-by-query-context]] === Update by query context Use a Painless script in an {ref}/docs-update-by-query.html[update by query] operation to add, modify, or delete fields within each of a set of documents collected as the result of query. *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. {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 finds all seats in a specific section that have not been sold and lowers the price by 2: [source,js] -------------------------------------------------- POST /seats/_update_by_query { "query": { "bool": { "filter": [ { "range": { "row": { "lte": 3 } } }, { "match": { "sold": false } }] } }, "script": { "source": "ctx._source.cost -= params.discount", "lang": "painless", "params": { "discount": 2 } } } -------------------------------------------------- // CONSOLE // TEST[setup:seats]