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I would like to only show posts that have "now and future" children using pre_get_posts action hook. Does anyone have an idea of how to achieve this?

function pre_get_posts($query) {        
    if(!is_admin() && $query->is_main_query()) {
        //check if the query matches this post type
        if(is_post_type_archive('event')) {
            $query->set('post_parent', 0); //only show parent posts
            //should only display posts that have children from now to future
        }
    }
}

All events with parent_id 0 should show but it should exclude events that have no children events linked to it.

Example:

  • Event 1 has 5 children. (include)
  • Event 2 has no children. (exclude)
  • Event 3 has 2 children. (include)
  • Event 4 has 1 child. (include)
  • Event 5 has no children. (exclude)

I have not yet found anything useful but will keep on looking for solutions.

Thank you for any responses.

  • All you need to do is find the ID of your "now to future" page and substitute the 0 for that. To find the ID, edit the page in the admin area and look in the address bar for post=xx - .../wp-admin/post.php?post=50&action=edit – David Gard Feb 23 '15 at 13:34
  • My apologies. I might not have posted it clear. All events with parent_id of 0 should show but it should exclude the events without child events linked to it. – Kobus Beets Feb 23 '15 at 13:39
  • Do you want the children listed as well, or just the parents? – David Gard Feb 23 '15 at 14:06
  • @DavidGard , i think he doesn't want to list children as he is setting post_parent to 0 – bravokeyl Feb 23 '15 at 14:46
  • That's my guess too (see answer), but it's always good to check ;-) – David Gard Feb 23 '15 at 14:48
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Before amending $query we first have to find out which posts to exclude, which requres two querys (if I can think of a way of doing it in one I'll update the answer).

The first will grab a list of distinct ID's of all parent events, for example -

SELECT DISTINCT wp_posts.post_parent FROM wp_posts WHERE wp_posts.post_type = "event" AND wp_posts.post_type = "publish" AND wp_posts.post_parent != 0

The next will grab the ID of all top-level events that do not have any children (so those that are not in the list we generated with the previous query), for example -

SELECT fgw_2_posts.ID FROM wp_posts WHERE wp_posts.post_type = "event" AND wp_posts.post_type = "publish" AND wp_posts.post_parent = 0 AND wp_posts.ID NOT IN (1,2,3)

Finally we can set the $query as required -

$query->set('post__not_in', $loners);
$query->set('post_parent', 0);

Here is the full code -

add_action('pre_get_posts', 'my_exclude_parents_without_children');
function my_exclude_parents_without_children($query){

    global $wpdb;

    if($query->is_main_query() && !is_admin()) :

        if(is_post_type_archive('event')) :

            /** First grab the ID's of all post parents */
            $my_query = $wpdb->prepare('SELECT DISTINCT %1$s.post_parent FROM %1$s WHERE %1$s.post_type = "event" AND %1$s.post_status = "publish" AND %1$s.post_parent != 0', $wpdb->posts);
            $parents = $wpdb->get_col($my_query);

            /** Next grab the ID of all posts who do not have children (we'll call them 'loners') */
            $my_query = $wpdb->prepare('SELECT %1$s.ID FROM %1$s WHERE %1$s.post_type = "event" AND %1$s.post_status = "publish" AND %1$s.post_parent = 0', $wpdb->posts, join(',', $parents));
            if(!empty($parents)) : // Ensure that there are events with children to exclude from this query
                $my_query.= $wpdb->prepare(' AND %1$s.ID NOT IN (%2$s)', $wpdb->posts, join(',', $parents));
            endif;
            $loners = $wpdb->get_col($my_query);

            /** Now exclude the 'loners' */
            $query->set('post__not_in', $loners);
            $query->set('post_parent', 0);

        endif;

    endif;

}
| improve this answer | |
  • please make sure to check for admin pages ( !is_admin ) as it effects edit.php?... – bravokeyl Feb 23 '15 at 14:44
  • @bravokeyl - Ah yes, there is a bug if I remember correctly. is_post_type_archive() should only work front end, but I've edited my answer to take account of this any way. – David Gard Feb 23 '15 at 14:47
  • 1
    For anyone who is interested, this defect was closed as invalid because, while not typically used in the admin area, conditional tags such as is_post_type_archive() are expected to work - core.trac.wordpress.org/ticket/18993. – David Gard Feb 23 '15 at 14:57
  • is_post_type_archive('wpse') also returns true when you are in edit.php?post_type='wpse' . – bravokeyl Feb 23 '15 at 14:57
  • @DavidGard That is a perfect solution for me. You are awesome. I did correct one thing though but it a minor. WHERE %1$s.post_type = "event" AND %1$s.post_status = "publish". Thanks again to all who helped out. – Kobus Beets Feb 24 '15 at 5:41

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