I believe this was just answered on the wp-hackers list but, for the record:
function apply_my_template( $postID, $post ) {
if (
!current_user_can( 'edit_post', $postID )
|| 'page' != $post->post_type
|| wp_is_post_revision( $postID )
|| wp_is_post_autosave( $postID )
|| 'auto-draft' == $post->post_status
|| 'trash' == $post->post_status
)
return $postID;
if ( 49 == $post->post_parent )
update_post_meta( $postID, '_wp_page_template',
'page-my-template.php' );
}
add_action( 'save_post', 'apply_my_template', 10, 2 );
Mixing some functions from here and here I wrote the code below in my functions.php:
function the_slug($pageID) { // Is there any other way to get the parent page slug?
$post_data = get_post($pageID, ARRAY_A);
$slug = $post_data['post_name'];
return $slug;
}
function child_page_template(){
global $post;
$parent_page_slug = the_slug($post->post_parent);
$page_template = 'page-'. $parent_page_slug . '-child.php'; //name it on your own
$parents = get_post_ancestors($post->ID); // if is child
if($parents){update_post_meta($post->ID,'_wp_page_template',$page_template);}
}
add_action('save_post','child_page_template');
Now, every time a child page is created or updated it will have as page template a file named “page-parentslug-child.php.
for example:
‘PARENT’ => page-slug.php (default)
‘parent’> ‘CHILD’ => page-‘PARENTSLUG’-child.php
‘parent’> ‘child’> ‘GRANDCHILD’ => page-‘CHILDSLUG’-child.php
‘parent’> ‘child’> ‘grandchild’ > ‘GRAND-GRANDCHILD’ => page-‘GRANDCHILDSLUG’-child.php (…) and so on.
That it
