register_rest_field( string|array $object_type, string $attribute, array $args = array() )

Registers a new field on an existing WordPress object type.


Object(s) the field is being registered to, "post"|"term"|"comment" etc.
The attribute name.
An array of arguments used to handle the registered field.
  • get_callback callable|null
    Optional. The callback function used to retrieve the field value. Default is 'null', the field will not be returned in the response. The function will be passed the prepared object data.
  • update_callback callable|null
    Optional. The callback function used to set and update the field value. Default is 'null', the value cannot be set or updated. The function will be passed the model object, like WP_Post.
  • schema array|null
    Optional. The schema for this field.
    Default is 'null', no schema entry will be returned.



function register_rest_field( $object_type, $attribute, $args = array() ) {
	global $wp_rest_additional_fields;

	$defaults = array(
		'get_callback'    => null,
		'update_callback' => null,
		'schema'          => null,

	$args = wp_parse_args( $args, $defaults );

	$object_types = (array) $object_type;

	foreach ( $object_types as $object_type ) {
		$wp_rest_additional_fields[ $object_type ][ $attribute ] = $args;



User Contributed Notes

  1. Skip to note 8 content

    GET callbacks accept up to 4 arguments in order…

    • $post – (object) Post or custom post type object of the request.
    • $attr – (string) Rest field/attr string identifier from the second parameter of your register_rest_field() declaration.
    • $request – (object) Full request payload – as a WP_REST_Request object
    • $object_type – (string) The object type which the field is registered against. Typically first parameter of your register_rest_field() declaration.

    Post callbacks accept the above arguments but also a 5th argument in the first position which is the value being passed from the POST request to the attribute/field.

  2. Skip to note 9 content

    To make use of sanitize_callback and validate_callback, pass those in arg_options in schema

    // Make sure to use PHP >= 5.4
    	function () {
    		// Field name to register.
    		$field = 'my_field';
    				'get_callback'    => function ( $object ) use ( $field ) {
    					// Get field as single value from post meta.
    					return get_post_meta( $object['id'], $field, true );
    				'update_callback' => function ( $value, $object ) use ( $field ) {
    					// Update the field/meta value.
    					update_post_meta( $object->ID, $field, $value );
    				'schema'          => array(
    					'type'        => 'string',
    					'arg_options' => array(
    						'sanitize_callback' => function ( $value ) {
    							// Make the value safe for storage.
    							return sanitize_text_field( $value );
    						'validate_callback' => function ( $value ) {
    							// Valid if it contains exactly 10 English letters.
    							return (bool) preg_match( '/\A[a-z]{10}\Z/', $value );
  3. Skip to note 10 content

    An example to add all of the post meta to a post-meta-fields field:

    add_action( 'rest_api_init', 'create_api_posts_meta_field' );
    function create_api_posts_meta_field() {
    	// register_rest_field ( 'name-of-post-type', 'name-of-field-to-return', array-of-callbacks-and-schema() )
    	register_rest_field( 'post', 'post-meta-fields', array(
    	       'get_callback'    => 'get_post_meta_for_api',
    	       'schema'          => null,
    function get_post_meta_for_api( $object ) {
    	//get the id of the post object array
    	$post_id = $object['id'];
    	//return the post meta
     	return get_post_meta( $post_id );

    This can be extended or edited. For example, if you don’t want to include all the post meta, you can filter it, or return only the field you need. The options are limitless, but the callback gives you access to the post object, which exposes the id among other parameters, so you can use many different helper functions.

  4. Skip to note 11 content

    This code works (also with shipped Backbone client) in WordPress 4.9.4:

    $meta = [
        'key' => 'my_post_type_name',
        'description' => 'This is the name of my post type',
        'type' => 'string'
    \register_rest_field('my_post_type', $meta['key'], [
        'get_callback' => function ($params) use ($meta) {
            return \get_post_meta($params['id'], $meta['key'], true);
        'update_callback' => function ($value, $object, $fieldName){
            return \update_post_meta($object->ID, $fieldName, $value);
  5. Skip to note 12 content

    An example to add post featured image src to the ‘featured_image_src’ field.

    add_action( 'rest_api_init', function () {
    	register_rest_field( 'post', 'featured_image_src', array(
    		'get_callback' => function ( $post_arr ) {
    			$image_src_arr = wp_get_attachment_image_src( $post_arr['featured_media'], 'medium' );
    			return $image_src_arr[0];
    		'update_callback' => null,
    		'schema' => null
    	) );
    } );

    Helpful for showing featured image in gutenberg block development when posts are fetched with withSelect() function.

  6. Skip to note 13 content

    Custom sql queries can be achieved to get whatever value you want from database. The following queries shows how can we modify rest output to show something from our custom table ‘wp_it_job_details’ which is, of course, inside WordPress database. Put it in your themes/plugins functions.php

    function add_last_date_data() {
      //Last date
      register_rest_field( 'post',
            'get_callback'  => 'rest_get_last_date',
            'update_callback'   => null,
            'schema'            => null,
    function rest_get_last_date( $object ) {
        //get the Post Id
        $post_id = $object['id'];
    	global $wpdb;
    	$sql = "SELECT * FROM wp_it_job_details WHERE post_id = '$post_id'"; //wp_it_job_details is job table
    	$results = $wpdb->get_row($sql);
    		if(count($results) > 0) {
    			//We have this post_id row in the table
    			return $results->last_date;	//last_date is the column name, change to your's
    		} else return ""; //return nothing 
    add_action( 'rest_api_init', 'add_last_date_data' );
  7. Skip to note 14 content
    // assume there custom post_type named events 
    add_action( 'rest_api_init', function() {
        register_rest_field( 'events', 'event_date', array(
            'get_callback' => function( $comment_arr ) {
                $comment_obj = get_field('event_date', $comment_arr['id'] );
                return $comment_obj;
            'update_callback' => function( $karma, $comment_obj ) {
                update_field('event_date', $karma, $comment_arr['id'] );
                return true;
            'schema' => array(
                'event_date' => __( 'event_date' ),
                'type'        => 'text'

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