How to solve this without flushing the rewrite rules for each post query the visitor triggers?

Question

Actually I have the problem that I provide a menu link (predefined in theme) to the latest post of a specific custom post type. I achieve this by the following function …

function get_latest_magazine_issue_url() {
    global $wpdb;
    $query = "SELECT ID FROM {$wpdb->prefix}posts WHERE post_type='magazine_issue' AND post_status='publish' ORDER BY post_date DESC LIMIT 1;";
    $result = $wpdb->get_results($query);
    if(is_object($result[0])) { return get_permalink($result[0]->ID); } 
    else { return ''; };
}

… fine til that point – but I recognized, that when I clicked on that link after adding a new cpt post, the link will still grab the post which was the latest when I implemented this link via widget. Is there any way to get around this without a flush_rewrite_rules() call? I wouldn't like to flush that way cause the codex says: http://codex.wordpress.org/Function_Reference/flush_rewrite_rules

Answer 1

Oh, the comment on your question makes it clear. In case you would like to always return a fresh latest post, no matter the page with menu link gets or not refreshed must be solved in another way.

At first: Create new page, let's say: "Latest post" - note it's ID.

And than add this into your functions.php:

function binda_redirect_to_latest( $query ) {
    $page_id = 234; //ID of your page with Latest post
    if ( $query->is_page( $page_id ) && $query->is_main_query() ) {          
        $args = array( 'numberposts' => 1, 'orderby' => 'post_date', 'order' => 'DESC', 'post_type' => 'magazine_issue', 'post_status' => 'publish' ); 
        $latest_post = get_posts( $args ); 
        foreach( $latest_post as $p ){
            $query->set( 'p', $p->ID );
            $query->set( 'page_id', '' );   
        }     
    }
    return $query;
}
add_action( 'pre_get_posts', 'binda_redirect_to_rand' );

Voilá

If you do not want to create an extra page, you can register a new query variable and chceck for it's present in pre_get_posts hook. This way:

add_filter( 'query_vars', 'my_query_vars' );
function my_query_vars( $vars ) {
    $vars[] = 'latest_post';
    return $vars;
}

Modified pre_get_posts hook callback:

function binda_redirect_to_latest( $query ) {    
    if ( $query->is_home() && isset($query->query_vars['latest_post']) && $query->query_vars['latest_post'] == 1 && $query->is_main_query() ) {          
        $args = array( 'numberposts' => 1, 'orderby' => 'post_date', 'order' => 'DESC', 'post_type' => 'magazine_issue', 'post_status' => 'publish' ); 
        $latest_post = get_posts( $args ); 
        foreach( $latest_post as $p ){
            $query->set( 'p', $p->ID );  
        }     
    }
    return $query;
}
add_action( 'pre_get_posts', 'binda_redirect_to_rand' );

To create a ling, you add_query_arg:

echo add_query_arg( 'latest_post', 1, get_bloginfo('url') );