register_meta( string $object_type, string $meta_key, array $args, string|array $deprecated = null )

Registers a meta key.


Description Description

It is recommended to register meta keys for a specific combination of object type and object subtype. If passing an object subtype is omitted, the meta key will be registered for the entire object type, however it can be partly overridden in case a more specific meta key of the same name exists for the same object type and a subtype.

If an object type does not support any subtypes, such as users or comments, you should commonly call this function without passing a subtype.


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Parameters Parameters

$object_type

(string) (Required) Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user', or any other object type with an associated meta table.

$meta_key

(string) (Required) Meta key to register.

$args

(array) (Required) Data used to describe the meta key when registered.

  • 'object_subtype'
    (string) A subtype; e.g. if the object type is "post", the post type. If left empty, the meta key will be registered on the entire object type. Default empty.
  • 'type'
    (string) The type of data associated with this meta key. Valid values are 'string', 'boolean', 'integer', 'number', 'array', and 'object'.
  • 'description'
    (string) A description of the data attached to this meta key.
  • 'single'
    (bool) Whether the meta key has one value per object, or an array of values per object.
  • 'default'
    (mixed) The default value returned from get_metadata() if no value has been set yet. When using a non-single meta key, the default value is for the first entry. In other words, when calling get_metadata() with $single set to false, the default value given here will be wrapped in an array.
  • 'sanitize_callback'
    (callable) A function or method to call when sanitizing $meta_key data.
  • 'auth_callback'
    (callable) Optional. A function or method to call when performing edit_post_meta, add_post_meta, and delete_post_meta capability checks.
  • 'show_in_rest'
    (bool|array) Whether data associated with this meta key can be considered public and should be accessible via the REST API. A custom post type must also declare support for custom fields for registered meta to be accessible via REST. When registering complex meta values this argument may optionally be an array with 'schema' or 'prepare_callback' keys instead of a boolean.

$deprecated

(string|array) (Optional) Deprecated. Use $args instead.

Default value: null


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Return Return

(bool) True if the meta key was successfully registered in the global array, false if not. Registering a meta key with distinct sanitize and auth callbacks will fire those callbacks, but will not add to the global registry.


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Source Source

File: wp-includes/meta.php

function register_meta( $object_type, $meta_key, $args, $deprecated = null ) {
	global $wp_meta_keys;

	if ( ! is_array( $wp_meta_keys ) ) {
		$wp_meta_keys = array();
	}

	$defaults = array(
		'object_subtype'    => '',
		'type'              => 'string',
		'description'       => '',
		'default'           => '',
		'single'            => false,
		'sanitize_callback' => null,
		'auth_callback'     => null,
		'show_in_rest'      => false,
	);

	// There used to be individual args for sanitize and auth callbacks.
	$has_old_sanitize_cb = false;
	$has_old_auth_cb     = false;

	if ( is_callable( $args ) ) {
		$args = array(
			'sanitize_callback' => $args,
		);

		$has_old_sanitize_cb = true;
	} else {
		$args = (array) $args;
	}

	if ( is_callable( $deprecated ) ) {
		$args['auth_callback'] = $deprecated;
		$has_old_auth_cb       = true;
	}

	/**
	 * Filters the registration arguments when registering meta.
	 *
	 * @since 4.6.0
	 *
	 * @param array  $args        Array of meta registration arguments.
	 * @param array  $defaults    Array of default arguments.
	 * @param string $object_type Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user',
	 *                            or any other object type with an associated meta table.
	 * @param string $meta_key    Meta key.
	 */
	$args = apply_filters( 'register_meta_args', $args, $defaults, $object_type, $meta_key );
	unset( $defaults['default'] );
	$args = wp_parse_args( $args, $defaults );

	// Require an item schema when registering array meta.
	if ( false !== $args['show_in_rest'] && 'array' === $args['type'] ) {
		if ( ! is_array( $args['show_in_rest'] ) || ! isset( $args['show_in_rest']['schema']['items'] ) ) {
			_doing_it_wrong( __FUNCTION__, __( 'When registering an "array" meta type to show in the REST API, you must specify the schema for each array item in "show_in_rest.schema.items".' ), '5.3.0' );

			return false;
		}
	}

	$object_subtype = ! empty( $args['object_subtype'] ) ? $args['object_subtype'] : '';

	// If `auth_callback` is not provided, fall back to `is_protected_meta()`.
	if ( empty( $args['auth_callback'] ) ) {
		if ( is_protected_meta( $meta_key, $object_type ) ) {
			$args['auth_callback'] = '__return_false';
		} else {
			$args['auth_callback'] = '__return_true';
		}
	}

	// Back-compat: old sanitize and auth callbacks are applied to all of an object type.
	if ( is_callable( $args['sanitize_callback'] ) ) {
		if ( ! empty( $object_subtype ) ) {
			add_filter( "sanitize_{$object_type}_meta_{$meta_key}_for_{$object_subtype}", $args['sanitize_callback'], 10, 4 );
		} else {
			add_filter( "sanitize_{$object_type}_meta_{$meta_key}", $args['sanitize_callback'], 10, 3 );
		}
	}

	if ( is_callable( $args['auth_callback'] ) ) {
		if ( ! empty( $object_subtype ) ) {
			add_filter( "auth_{$object_type}_meta_{$meta_key}_for_{$object_subtype}", $args['auth_callback'], 10, 6 );
		} else {
			add_filter( "auth_{$object_type}_meta_{$meta_key}", $args['auth_callback'], 10, 6 );
		}
	}

	if ( array_key_exists( 'default', $args ) ) {
		$schema = $args;
		if ( is_array( $args['show_in_rest'] ) && isset( $args['show_in_rest']['schema'] ) ) {
			$schema = array_merge( $schema, $args['show_in_rest']['schema'] );
		}

		$check = rest_validate_value_from_schema( $args['default'], $schema );
		if ( is_wp_error( $check ) ) {
			_doing_it_wrong( __FUNCTION__, __( 'When registering a default meta value the data must match the type provided.' ), '5.5.0' );

			return false;
		}

		if ( ! has_filter( "default_{$object_type}_metadata", 'filter_default_metadata' ) ) {
			add_filter( "default_{$object_type}_metadata", 'filter_default_metadata', 10, 5 );
		}
	}

	// Global registry only contains meta keys registered with the array of arguments added in 4.6.0.
	if ( ! $has_old_auth_cb && ! $has_old_sanitize_cb ) {
		unset( $args['object_subtype'] );

		$wp_meta_keys[ $object_type ][ $object_subtype ][ $meta_key ] = $args;

		return true;
	}

	return false;
}


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Changelog Changelog

Changelog
Version Description
5.5.0 The $default argument was added to the arguments array.
5.3.0 Valid meta types expanded to include "array" and "object".
4.9.8 The $object_subtype argument was added to the arguments array.
4.6.0 Modified to support an array of data to attach to registered meta keys. Previous arguments for $sanitize_callback and $auth_callback have been folded into this array.
3.3.0 Introduced.

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User Contributed Notes User Contributed Notes

  1. Skip to note 2 content
    Contributed by michielve

    As of Wordpress 4.9.8 you can use the object_subtype parameter to specify a custom post type. Previously you could only register for all post types. For example to register a meta key my_meta for only the my_article custom post type:

    register_meta('post', 'my_meta', [
      'object_subtype' => 'my_article',
      'show_in_rest' => true
    ]);

    Or you can use the new register_post_meta function.

  2. Skip to note 3 content
    Contributed by tharsheblows

    As of WordPress 4.7, you can use the function as follows. This will be expanded in future versions.

    $object_type = 'post'; // The object type. 
    	// For custom post types, this is 'post', for custom comment types, this is 'comment'.
    
    $args1 = array(
        'type'		=> 'string', // Validate and sanitize the meta value as a string.
    		// Default: 'string'.  
        	// In 4.7 one of 'string', 'boolean', 'integer', 'number' must be used as 'type'. 
        'description'    => 'A meta key associated with a string meta value.', // Shown in the schema for the meta key.
        'single'        => true, // Return a single value of the type. Default: false.
        'show_in_rest'    => true, // Show in the WP REST API response. Default: false.
    );
    
    register_meta( $object_type, 'my_postmeta_key', $args1 );
    
    
    $args2 = array(
        'type'             => 'string', // Validate and sanitize the meta value as a string.
        'description'    => 'A meta key associated with a string meta value.', // Shown in the schema for the meta key.
        'single'        => false, // Return an array with the type used as the items type. Default: false.
        'show_in_rest'    => true, // Show in the WP REST API response. Default: false.
    );
    
    register_meta( 'user', 'my_usermeta_key', $args2 );

    This will return the meta key and meta value in the meta object in the response. For example, an individual post response where id=8 and a meta key `my_postmeta_key` as registered above:

    {
      "id": 8, // the post id
     	...
      "meta": {
        "my_postmeta_key": "the meta value"
      },
    	...
    }
  3. Skip to note 5 content

    For custom meta fields to be returned in the REST API for a custom post type the REST API Handbook notes that the post type must support custom-fields in order for the registered meta field to display.

    From the handbook:

    “Note that for meta fields registered on custom post types, the post type must have custom-fields support. Otherwise the meta fields will not appear in the REST API.”

    Source: https://developer.wordpress.org/rest-api/extending-the-rest-api/modifying-responses/#read-and-write-a-post-meta-field-in-post-responses

  4. Skip to note 7 content
    Contributed by Aniket

    Prior to WordPress 5.5, the defaults for a custom meta field to be made available to the REST API could only be achieved like this:

    (Consider registering a custom checkbox field for certain user input – for example, a post type title toggle)

    register_meta(
         'post',
         '_custom_meta_key',
         array(
             'single'       => true,
             'type'         => 'boolean', // or any valid data type
             'show_in_rest' => array(
                 'schema' => array(
                     'type'  => 'boolean', // Should match the expected data type
                     'default' => true,
                 ),
             ),
         )
     );

    With WordPress 5.5, this could be done with the additional argument default, like this:

    register_meta(
         'post',
         '_custom_meta_key',
         array(
             'single'       => true,
             'type'         => 'boolean',
             'default'      => true, // this is what really does the trick instead of supplying REST schema
             'show_in_rest' => true,
         )
     );

    Worth noting, this could really be helpful while extending block editor sidebar to make custom fields available via custom meta boxes. Setting default values for custom fields in the block editor is not straightforward, otherwise.

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