Update postmeta after theme switch

Question

I am trying to update the postmeta table when I switch themes. I am updating the metavalue to be template-name.themename.php.

However, this only works with the default themes in wordpress.

If I go to add a new theme, and activate that, it does not work.

The metavalue updates correctly, but the new theme is overriding the custom template.

Here is the code I have.

    <?php
    add_action('after_switch_theme', 'update_templates');

    function update_templates() {

    global $wpdb;
    $new_template = "pl-template.". strtolower(trim(get_current_theme())) .".php";
    $pl_pages = $wpdb->get_results(" SELECT * FROM {$wpdb->prefix}posts WHERE pevo_page = 1");


    foreach ( $pl_pages as $pages) {

        $post_id = $pages->ID;

        $wpdb->query(  
            "
                UPDATE {$wpdb->prefix}postmeta
                SET meta_value = '$new_template'
                WHERE post_id = $post_id                         
            "
         );

    }
}
    ?>

The custom template, is just blank right now and just displays the page title

    <?php
    /*
     Template Name: Template Name
    */


    $the_title = get_the_title();

    echo $the_title;
   ?>

working code thanks to the answers, I used an array because this is within my plugin class.

    add_filter( 'template_include', array($this, 'plugin_page_templates')); 


          function plugin_page_templates() {
    global $wpdb;
    $pagename = get_the_title();
    $ispluginpage = $wpdb->get_var("SELECT plugin_page FROM {$wpdb->prefix}posts WHERE post_title = '$pagename'");

    if ($ispluginpage == 1) {
        return plugin_dir_path( __FILE__ ) . 'includes/plugin-template.php';
    }

    return $template;
          }

Answer 1

I am going to guess that you have your code in the theme, probably functions.php. That code will only load when the theme is active, and after_switch_theme only runs after the theme change. There is no before_switch_theme that I am aware of.

You will need to have this code in a plugin or a mu-plugin file in order to have it work for all themes.

But don't...

This kind of template highjacking is going to make whatever you are doing very unpopular. Not to mention that it is a very messy way to do things. You are altering database values that you are going to have to eventually clean up again.

Though it is not clear why you need to do this, or even exactly what the end result is supposed to be, I am pretty sure that they right way to do it is with the template_include and/or template_redirect hooks.

For usage examples:

https://wordpress.stackexchange.com/search?q=user%3A21376+template_include
https://wordpress.stackexchange.com/search?q=user%3A21376+template_redirect