get post ancestors function doesn't work?!

Hello everyone,

I’m trying to display breadcrumbs for a page. I’m using get_post_ancestors() function, but it returns an empty array, even though there is definately a parent. Also, I’ve testing it with $post->ancestors which returns an array with page’s parent ID … but get_post_ancestors() still returns an empty array.

Does anyone know what might be a problem??

I’m using the following function in my functions.php This is simplified version of code I found in Codex https://codex.www.ads-software.com/Function_Reference/wp_list_pages#List_current_Page.2C_ancestors_of_current_page.2C_and_children_of_current_page

<?php
function breadcrumbs() {
	global $post;
	//if the post has a parent
	if($post->post_parent){
	  //collect ancestor pages
	  $relations = get_post_ancestors($post->ID);
	  //add current post to pages
	  array_push($relations, $post->ID);
	  //get comma delimited list of children and parents and self
	  $relations_string = implode(",",$relations);
	  //use include to list only the collected pages.
	  $sidelinks = wp_list_pages("title_li=&echo=0&include=".$relations_string);
	}
	if ($sidelinks) { ?>
	<div id="breadcrumbs">
		<div class="page-title-inner">
			<ul>
				<?php
				//links in <li> tags
				echo $sidelinks; ?>
			</ul>
		</div>
	</div>
	<?php }
} ?>

And then I call breadcrumbs() function from my theme templates:

<?php breadcrumbs(); ?>

Thanks,
Dasha