After three days of struggling and posting a question here I managed to find an answer. Yeh I know… To my defense I can say that it’s my first WP project. I did it this way:
$exclude = get_excluded_parents();
$parents = get_posts(
array(
'post_type' => 'jhk_story',
'orderby' => 'ID',
'order' => 'ASC',
'numberposts' => -1,
'exclude' => $exclude,
)
);
The rest of the code here ...
}
} // story_frame_attributes_meta_box()
/*
* Filters excluded parents from post_type: story_frame
*/
function get_excluded_parents() {
// Select all posts with post_type = story_frame
$childs = get_posts (
array (
'post_type' => 'story_frame',
'orderby' => 'ID',
'order' => 'ASC',
'numberposts' => -1
)
);
$exclude = array();
foreach ( $childs as $child ) {
if ( 0 < $child->post_parent ) {
array_push( $exclude, $child->post_parent );
}
} // foreach $child
return $exclude;
} // get_excluded_parents()
Hope someone will benefit from it.