当您选择页面模板时，WordPress会使用键将其存储为Posteta_wp_page_template. 存储的值是相对于模板目录（或样式表目录）的实际页面模板路径。

因此，当WP查找要包含的模板时，它将somefilename.php 当它找不到它时，它会回到page.php.

您可以在函数中看到WP搜索的文件get_page_template 和get_page_template_slug

<?php
// in wp-includes/template.php
/**
 * Retrieve path of page template in current or parent template.
 *
 * Will first look for the specifically assigned page template
 * The will search for \'page-{slug}.php\' followed by \'page-id.php\'
 * and finally \'page.php\'
 *
 * @since 1.5.0
 *
 * @return string
 */
function get_page_template() {
    $id = get_queried_object_id();
    $template = get_page_template_slug();
    $pagename = get_query_var(\'pagename\');

    if ( ! $pagename && $id ) {
        // If a static page is set as the front page, $pagename will not be set. Retrieve it from the queried object
        $post = get_queried_object();
        $pagename = $post->post_name;
    }

    $templates = array();
    if ( $template && 0 === validate_file( $template ) )
        $templates[] = $template;
    if ( $pagename )
        $templates[] = "page-$pagename.php";
    if ( $id )
        $templates[] = "page-$id.php";
    $templates[] = \'page.php\';

    return get_query_template( \'page\', $templates );
}

// in wp-includes/post-template.php
/**
 * Get the specific template name for a page.
 *
 * @since 3.4.0
 *
 * @param int $id The page ID to check. Defaults to the current post, when used in the loop.
 * @return string|bool Page template filename. Returns an empty string when the default page template
 *  is in use. Returns false if the post is not a page.
 */
function get_page_template_slug( $post_id = null ) {
    $post = get_post( $post_id );
    if ( \'page\' != $post->post_type )
        return false;
    $template = get_post_meta( $post->ID, \'_wp_page_template\', true );
    if ( ! $template || \'default\' == $template )
        return \'\';
    return $template;
}

<?php
add_filter(\'page_template\', \'wpse57568_page_template\');
function wpse57568_page_template($t)
{
    $old_slug = \'pages/t.php\'; // replace this
    $new_slug = \'pages/new.php\'; // replace this

    $page_id = get_queried_object_id();
    $template = get_post_meta($page_id, \'_wp_page_template\', true);
    if($template && \'default\'!= $template && $old_slug == $template)
    {
        if(file_exists(trailingslashit(STYLESHEETPATH) . $new_slug))
        {
            $t = trailingslashit(STYLESHEETPATH) . $new_slug;
        }
        elseif(file_exists(trailingslashit(TEMPLATEPATH) . $new_slug))
        {
            $t = trailingslashit(TEMPLATEPATH) . $new_slug;
        }
    }
    return $t;
}