Source
File: wp-includes/meta.php
function get_registered_metadata( $object_type, $object_id, $meta_key = '' ) {
$object_subtype = get_object_subtype( $object_type, $object_id );
if ( ! empty( $meta_key ) ) {
if ( ! empty( $object_subtype ) && ! registered_meta_key_exists( $object_type, $meta_key, $object_subtype ) ) {
$object_subtype = '';
}
if ( ! registered_meta_key_exists( $object_type, $meta_key, $object_subtype ) ) {
return false;
}
$meta_keys = get_registered_meta_keys( $object_type, $object_subtype );
$meta_key_data = $meta_keys[ $meta_key ];
$data = get_metadata( $object_type, $object_id, $meta_key, $meta_key_data['single'] );
return $data;
}
$data = get_metadata( $object_type, $object_id );
if ( ! $data ) {
return array();
}
$meta_keys = get_registered_meta_keys( $object_type );
if ( ! empty( $object_subtype ) ) {
$meta_keys = array_merge( $meta_keys, get_registered_meta_keys( $object_type, $object_subtype ) );
}
return array_intersect_key( $data, $meta_keys );
}