Use a variable in Custom Post Type permalink

Hey,

i have a permalink issue but i don’t know to solve it.
I want to use a variable in my custom post type permalinks like:
https://www.domain.com/variable/postname
This is all i want and i don’t can’t solve it.

I have try it with this code but always i become a 404 Error.

function post_type_profiles() {
		register_post_type ( 'custompost',
	                array (
	                    'label' => __('custompost'),
	                    'public' => true,
	                    'show_ui' => true,
			    'has_archive' => true,
			    'hierarchical' => true,
			    'rewrite' => array(
			          'with_front' => false,
				   'slug' => '%city%'
								    ),
	                    'supports' => array (
		            	'title',
			    	'editor',
	                    	'post-thumbnails',
	                    	'revisions'
							)
	                )
	        );
	}
add_action('init', 'post_type_profiles');

add_filter('post_type_link', 'custompost_permalink', 1, 3);
function custompost_permalink($post_link, $id = 0, $leavename) {
    global $wp_rewrite;
    global $wpdb;

    $post = &get_post($id);
    if ( is_wp_error( $post ) )
        return $post;

    $newlink = $wp_rewrite->get_extra_permastruct('custompost');
    $sql = "
        SELECT city
        FROM anydatabase
        WHERE post_id = " . $post->ID . "";
        $address = $wpdb->get_var($wpdb->prepare($sql));
	$city = str_replace(" ", "-", strtolower($address));
	$title = str_replace(" ", "-", strtolower(get_the_title( $post->ID )));
	$newlink = str_replace("%city%", $city, $newlink);
	$newlink = str_replace("%postname%", $title, $newlink);
	$newlink = home_url(user_trailingslashit($newlink));
	return $newlink;
}

add_action('init', 'myposttype_rewrite');
function myposttype_rewrite($post_link) {
    global $wp_rewrite;
    $queryarg = 'post_type=custompost&p=';
    $wp_rewrite->add_rewrite_tag('%city%', '([^/]+)', $queryarg);
    $wp_rewrite->add_permastruct('custompost', '%city%/%postname%.html');

}

Perhaps theres any other solution, so let me know to use a variable from my database in the permalink. I work many days on it and it doesn’t work now! ??