.. meta::
   :description: This document provides usage information for the Apache Kafka SMT org.apache.kafka.connect.transforms.ExtractField.

.. _extractfield:

============
ExtractField
============

The following provides usage information for the |ak-tm| SMT
``org.apache.kafka.connect.transforms.ExtractField``.

Description
-----------

``ExtractField`` pulls a field out of a complex (non-primitive, Map or Struct)
key or value and replaces the entire key or value with the extracted field. Any
``null`` values are passed through unmodified.

Use the concrete transformation type designed for the record key
(``org.apache.kafka.connect.transforms.ExtractField$Key``) or value
(``org.apache.kafka.connect.transforms.ExtractField$Value``).

Examples
--------

The following examples show how to use ``ExtractField`` by itself and in
conjunction with a second SMT.

------------------
Extract Field Name
------------------

The configuration snippet below shows how to use ``ExtractField`` to extract the
field name ``"id"``.

.. code-block:: json

   "transforms": "ExtractField",
   "transforms.ExtractField.type": "org.apache.kafka.connect.transforms.ExtractField$Value",
   "transforms.ExtractField.field": "id"

Before: ``{"id": 42, "cost": 4000}``

After: ``42``

.. tip::
   
   For additional examples, see `ExtractField <https://docs.confluent.io/cloud/current/connectors/single-message-transforms.html#extract-field>`__ for managed connectors.

Properties
----------

.. list-table::
   :header-rows: 1
   :widths: 15 30 10 10 10 10

   *  - Name
      - Description
      - Type
      - Default
      - Valid Values
      - Importance
   *  - ``field``
      - Field name to extract.
      - string
      -
      -
      - medium

.. include:: includes/Example_ValueToKeyExtractField.rst

.. include:: includes/predicate.rst