WP_REST_Meta_Fields::get_value( int $object_id, WP_REST_Request $request )

	public function get_value( $object_id, $request ) {
		$fields   = $this->get_registered_fields();
		$response = array();

		foreach ( $fields as $meta_key => $args ) {
			$name = $args['name'];
			$all_values = get_metadata( $this->get_meta_type(), $object_id, $meta_key, false );
			if ( $args['single'] ) {
				if ( empty( $all_values ) ) {
					$value = $args['schema']['default'];
				} else {
					$value = $all_values[0];
				}
				$value = $this->prepare_value_for_response( $value, $request, $args );
			} else {
				$value = array();
				foreach ( $all_values as $row ) {
					$value[] = $this->prepare_value_for_response( $row, $request, $args );
				}
			}

			$response[ $name ] = $value;
		}

		return $response;
	}