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I try to add auto increment post numbering by category. Like cat="myID" > post 1, post 2, post 3...

Display post number not post ID number

In find this solution, and use post_meta looks a good way. But this solution work only for all category. I try to change it like this, but it's doesn't work.

$querystr = "SELECT $wpdb->posts.* FROM $wpdb->posts 
             WHERE $wpdb->posts.post_status = 'publish' 
             AND $wpdb->posts.post_type = 'post' 
             AND $wpdb->posts.post_cat = '35'
             ORDER BY $wpdb->posts.post_date ASC"
  • Do you want to number posts (add meta field with ordinal number) in each category separately? What if the post will be in more than one category, what number should it receive? – nmr Aug 16 '18 at 17:04
  • I want show it for only one category. Yes you right, it's more difficult with several categories. – julien c Aug 17 '18 at 7:37
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Add this code to functions.php. It should add meta value to posts from given category.
You can use hardcoded category slug/ID, but maybe it would be better to store it in options table and allow to change from dashboard.

Change "ID" / "category_slug" to your own.

/**
 * @param int     $post_ID      Post ID.
 * @param WP_Post $post_after   Post object following the update.
 * @param WP_Post $post_before  Post object before the update.
 */
function updateNumbers($post_id, $post_after, $post_before) {
    global $wpdb;

    if ( $post_after->post_type != 'post' )
        return;

    $selected_cat_ID = 123; // <-- ID of your category with numbering

    // -- select category ID by slug --
    // $selected_cat = 'category_slug';
    // $selected_cat_ID = get_terms(['slug' => 'category_slug', 'fields'=> 'ids', 'taxonomy' => 'category', 'hide_empty' => false,]);
    // if ( !is_array($selected_cat_ID) || empty($selected_cat_ID) ) 
    //     return; 
    // $selected_cat_ID = $selected_cat_ID[0];
    // -- end: select category ID by slug --

    $incr_number = get_post_meta($post_id, 'incr_number', true);

    //
    // get posts assigned to your category
    $query = "SELECT p.id FROM {$wpdb->posts} p"
                . " LEFT JOIN {$wpdb->term_relationships} tr ON tr.object_id = p.id"
                . " LEFT JOIN {$wpdb->term_taxonomy} tt ON tt.term_taxonomy_id = tr.term_taxonomy_id"
                . " LEFT JOIN {$wpdb->terms} t ON t.term_id = tt.term_id"
            . " WHERE p.post_status = 'publish' AND p.post_type = 'post'"
            // if you want use slug instead ID change "AND t.term_id = %d" to "AND t.slug = %s"
            . " AND tt.taxonomy = 'category' AND t.term_id = %d"  
            . " ORDER BY p.post_date ASC";
    $ids = $wpdb->get_results( $wpdb->prepare($query, $selected_cat_ID), OBJECT );

    // is post assigned to category after update
    $in_category = false;
    $assigned_posts = [];

    foreach( $ids as $row ) {
        $assigned_posts[] = $row->id;
        if ( $row->id == $post_id )
            $in_category = true;
    }

    if ( !$in_category && $incr_number === '' ) {
        //
        // after the update post is not in the category, before the update was not either
        return;
    }
    else if ($in_category && $incr_number !== '' && $post_before->post_date_gmt == $post_after->post_date_gmt ) {
        //
        // after the update, post is still in the category,
        // publish date has not changed,
        // numbering doesn't need to be changed
        return;
    }
    else if ( !$in_category && $incr_number !== '' ) {
        //
        // post has he been removed from category
        delete_post_meta($post_id, 'incr_number');
    }

    // update numbering
    if ( !empty($assigned_posts) ) {
        $counts = 0;
        foreach( $assigned_posts as $pid )
            update_post_meta($pid, 'incr_number', ++$counts);
    }
}
add_action( 'post_updated', 'updateNumbers', 10, 3);
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There's no field in wp_posts called "post_cat".

Try "post_category" instead.

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