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

User Contributed Notes

1. Skip to note 10 content

   Jan-Willem 7 years ago

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   The values of $object_type are not documented but I found.
   post for all post types, term for all taxonomies.
   There might be other ‘objects’.
2. Skip to note 11 content

   michielve 6 years ago

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   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.
3. Skip to note 12 content

   Thomas Patrick Levy 5 years ago

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   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

   • This is also essential for saving values. If the post type doesn’t support custom-fields, the values will NOT be saved to the database.

     Mark Howells-Mead 2 years ago
4. Skip to note 13 content

   tharsheblows 8 years ago

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   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"
     },
   	...
   }
5. Skip to note 14 content

   Aniket Ashtikar 4 years ago

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   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.
6. Skip to note 15 content

   martinkolle 3 years ago

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   auth_callback and sanitize_callback is callable with arguments.

   Auth callback is applied in map_meta_cap() (wp-includes/capabilities.php).
   Sanitize callback is applied in sanitize_meta() (wp-includes/meta.php).

   $status = register_meta( 'post', '_candidate_title', array(
       'type' => 'string',
       'description' => 'event location',
       'object_subtype' => 'resume',
       'single' => true,
       'show_in_rest' => array(
           'schema' => array(
               'type' => 'string',
               'default' => true
           )
       ),
       'auth_callback' => function(  $allowed, $meta_key, $object_id, $user_id, $cap, $caps ) {
           return current_user_can( 'edit_resume', $object_id );
       },
       'sanitize_callback' => function( $meta_value, $meta_key, $object_type, $object_subtype ) {
           return $meta_value;
       }
   ) );
7. Skip to note 16 content

   Barry Ceelen 5 years ago

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   Note that for the ‘show_in_rest’ argument to take effect, the post type should be registered with ‘custom-fields’ support.
8. Skip to note 17 content

   kitchin 3 years ago

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   In WP Core, `register_meta() ` is only used by `register_post_meta` and `register_term_meta() `, and otherwise none of these functions are used in Core.

   Jetpack uses `register_post_meta() `, and `register_meta() ` for ‘post’ and ‘user’. So Jetpack has code samples to examine for their use.
9. Skip to note 18 content

   Codex 9 years ago

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   Basic Example

   <?php register_meta( 'post', 'my_registered_meta', 'my_sanitize_callback', '__return_false' ); ?>