Display children and grandchildren of a custom post type

Question

How do get the grandchildren to show up on the PARENT post, right now I can only get the children to show up on the parent post, and grandchildren on the child post.

I'd like to make a list this way:

Parent post (current page)
-Child 1
--grandchild 1
--grandchild 2
--grandchild 3
-Child 2
--grandchild 1
--grandchild 2
--grandchild 3

This is my code so far

<?php 
$args = array( 'post_parent' => get_the_ID(), 'post_type' => 'series', 'posts_per_page' => -1 );
$childs = new WP_Query( $args );
while ( $childs->have_posts() ) : $childs->the_post();
?>
<a href="<?php the_permalink(); ?>"><?php the_title(); ?></a>

<?php endwhile;  wp_reset_postdata(); ?>

Any help is appreciated, thank you!

Update:

<ul>Child1 title
<li>grandchild</li>
<li>grandchild2</li>
<li>grandchild3</li>
</ul>
<ul>Child2 title
<li>grandchild</li>
<li>grandchild2</li>
<li>grandchild3</li>
</ul>

Answer 1

You can create walker for the wp_list_pages() this function use the Walker_Page you can extends him.

Walker fo example you put it in the functions.php I added comments with the class name No_Link_First_Child_Walker so you could see what I changed you can search for them.

class No_Link_First_Child_Walker extends Walker_Page {
    public function start_el( &$output, $page, $depth = 0, $args = array(), $current_page = 0 ) {
        if ( isset( $args['item_spacing'] ) && 'preserve' === $args['item_spacing'] ) {
            $t = "\t";
            $n = "\n";
        } else {
            $t = '';
            $n = '';
        }
        if ( $depth ) {
            $indent = str_repeat( $t, $depth );
        } else {
            $indent = '';
        }

        $css_class = array( 'page_item', 'page-item-' . $page->ID );

        if ( isset( $args['pages_with_children'][ $page->ID ] ) ) {
            $css_class[] = 'page_item_has_children';
        }

        if ( ! empty( $current_page ) ) {
            $_current_page = get_post( $current_page );
            if ( $_current_page && in_array( $page->ID, $_current_page->ancestors ) ) {
                $css_class[] = 'current_page_ancestor';
            }
            if ( $page->ID == $current_page ) {
                $css_class[] = 'current_page_item';
            } elseif ( $_current_page && $page->ID == $_current_page->post_parent ) {
                $css_class[] = 'current_page_parent';
            }
        } elseif ( $page->ID == get_option('page_for_posts') ) {
            $css_class[] = 'current_page_parent';
        }

        /**
         * Filters the list of CSS classes to include with each page item in the list.
         *
         * @since 2.8.0
         *
         * @see wp_list_pages()
         *
         * @param array   $css_class    An array of CSS classes to be applied
         *                              to each list item.
         * @param WP_Post $page         Page data object.
         * @param int     $depth        Depth of page, used for padding.
         * @param array   $args         An array of arguments.
         * @param int     $current_page ID of the current page.
         */
        $css_classes = implode( ' ', apply_filters( 'page_css_class', $css_class, $page, $depth, $args, $current_page ) );

        if ( '' === $page->post_title ) {
            /* translators: %d: ID of a post */
            $page->post_title = sprintf( __( '#%d (no title)' ), $page->ID );
        }

        $args['link_before'] = empty( $args['link_before'] ) ? '' : $args['link_before'];
        $args['link_after'] = empty( $args['link_after'] ) ? '' : $args['link_after'];

        $atts = array();
        $atts['href'] = get_permalink( $page->ID );

        /**
         * Filters the HTML attributes applied to a page menu item's anchor element.
         *
         * @since 4.8.0
         *
         * @param array $atts {
         *     The HTML attributes applied to the menu item's `<a>` element, empty strings are ignored.
         *
         *     @type string $href The href attribute.
         * }
         * @param WP_Post $page         Page data object.
         * @param int     $depth        Depth of page, used for padding.
         * @param array   $args         An array of arguments.
         * @param int     $current_page ID of the current page.
         */
        $atts = apply_filters( 'page_menu_link_attributes', $atts, $page, $depth, $args, $current_page );

        /**
         * No_Link_First_Child_Walker
         * Here I removed the the attribute for the href if the depth equal to 1
         */
        if($depth == 1) {
            unset($atts['href']);
        }

        $attributes = '';
        foreach ( $atts as $attr => $value ) {
            if ( ! empty( $value ) ) {
                $value = esc_attr( $value );
                $attributes .= ' ' . $attr . '="' . $value . '"';
            }
        }

        /**
         * No_Link_First_Child_Walker
         * Here I add a condition to check if depth is 1 so the tag will be span
         */
        $output .= $indent . sprintf(
            '<li class="%s">'.(($depth == 1) ? '<span%s>%s%s%s</span>' : '<a%s>%s%s%s</a>'),
            $css_classes,
            $attributes,
            $args['link_before'],
            /** This filter is documented in wp-includes/post-template.php */
            apply_filters( 'the_title', $page->post_title, $page->ID ),
            $args['link_after']
        );

        if ( ! empty( $args['show_date'] ) ) {
            if ( 'modified' == $args['show_date'] ) {
                $time = $page->post_modified;
            } else {
                $time = $page->post_date;
            }

            $date_format = empty( $args['date_format'] ) ? '' : $args['date_format'];
            $output .= " " . mysql2date( $date_format, $time );
        }
    }

}

Now you call the function wp_list_pages() with this walker too like this.

wp_list_pages(array('post_type'=>'series', 'walker'=>new No_Link_First_Child_Walker()));

Or you could make another while loop inside the second while for the grandchildren.

Try this

class No_Link_First_Child_Walker extends Walker_Page {
    /**
     * Outputs the beginning of the current level in the tree before elements are output.
     *
     * @since 2.1.0
     *
     * @see Walker::start_lvl()
     *
     * @param string $output Used to append additional content (passed by reference).
     * @param int    $depth  Optional. Depth of page. Used for padding. Default 0.
     * @param array  $args   Optional. Arguments for outputting the next level.
     *                       Default empty array.
     */
    public function start_lvl( &$output, $depth = 0, $args = array() ) {
        if ( isset( $args['item_spacing'] ) && 'preserve' === $args['item_spacing'] ) {
            $t = "\t";
            $n = "\n";
        } else {
            $t = '';
            $n = '';
        }
        $indent = str_repeat( $t, $depth );
        // No_Link_First_Child_Walker check depth and remove <ul> for depth 0
        if($depth !== 0) {
            $output .= "{$n}{$indent}<ul class='children'>{$n}";
        }
    }

    /**
     * Outputs the end of the current level in the tree after elements are output.
     *
     * @since 2.1.0
     *
     * @see Walker::end_lvl()
     *
     * @param string $output Used to append additional content (passed by reference).
     * @param int    $depth  Optional. Depth of page. Used for padding. Default 0.
     * @param array  $args   Optional. Arguments for outputting the end of the current level.
     *                       Default empty array.
     */
    public function end_lvl( &$output, $depth = 0, $args = array() ) {
        if ( isset( $args['item_spacing'] ) && 'preserve' === $args['item_spacing'] ) {
            $t = "\t";
            $n = "\n";
        } else {
            $t = '';
            $n = '';
        }
        $indent = str_repeat( $t, $depth );
        // No_Link_First_Child_Walker check depth and remove </ul> for depth 0
        if($depth !== 0) {
            $output .= "{$indent}</ul>{$n}";
        }

    }

    public function start_el( &$output, $page, $depth = 0, $args = array(), $current_page = 0 ) {

        if ( isset( $args['item_spacing'] ) && 'preserve' === $args['item_spacing'] ) {
            $t = "\t";
            $n = "\n";
        } else {
            $t = '';
            $n = '';
        }
        if ( $depth ) {
            $indent = str_repeat( $t, $depth );
        } else {
            $indent = '';
        }

        $css_class = array( 'page_item', 'page-item-' . $page->ID );

        if ( isset( $args['pages_with_children'][ $page->ID ] ) ) {
            $css_class[] = 'page_item_has_children';
        }

        if ( ! empty( $current_page ) ) {
            $_current_page = get_post( $current_page );
            if ( $_current_page && in_array( $page->ID, $_current_page->ancestors ) ) {
                $css_class[] = 'current_page_ancestor';
            }
            if ( $page->ID == $current_page ) {
                $css_class[] = 'current_page_item';
            } elseif ( $_current_page && $page->ID == $_current_page->post_parent ) {
                $css_class[] = 'current_page_parent';
            }
        } elseif ( $page->ID == get_option('page_for_posts') ) {
            $css_class[] = 'current_page_parent';
        }

        /**
         * Filters the list of CSS classes to include with each page item in the list.
         *
         * @since 2.8.0
         *
         * @see wp_list_pages()
         *
         * @param array   $css_class    An array of CSS classes to be applied
         *                              to each list item.
         * @param WP_Post $page         Page data object.
         * @param int     $depth        Depth of page, used for padding.
         * @param array   $args         An array of arguments.
         * @param int     $current_page ID of the current page.
         */
        $css_classes = implode( ' ', apply_filters( 'page_css_class', $css_class, $page, $depth, $args, $current_page ) );

        if ( '' === $page->post_title ) {
            /* translators: %d: ID of a post */
            $page->post_title = sprintf( __( '#%d (no title)' ), $page->ID );
        }

        $args['link_before'] = empty( $args['link_before'] ) ? '' : $args['link_before'];
        $args['link_after'] = empty( $args['link_after'] ) ? '' : $args['link_after'];

        $atts = array();
        $atts['href'] = get_permalink( $page->ID );

        /**
         * Filters the HTML attributes applied to a page menu item's anchor element.
         *
         * @since 4.8.0
         *
         * @param array $atts {
         *     The HTML attributes applied to the menu item's `<a>` element, empty strings are ignored.
         *
         *     @type string $href The href attribute.
         * }
         * @param WP_Post $page         Page data object.
         * @param int     $depth        Depth of page, used for padding.
         * @param array   $args         An array of arguments.
         * @param int     $current_page ID of the current page.
         */
        $atts = apply_filters( 'page_menu_link_attributes', $atts, $page, $depth, $args, $current_page );

        /**
         * No_Link_First_Child_Walker
         * Here I removed the the attribute for the href if the depth equal to 1
         */
        if($depth == 1) {
            unset($atts['href']);
        }

        $attributes = '';
        foreach ( $atts as $attr => $value ) {
            if ( ! empty( $value ) ) {
                $value = esc_attr( $value );
                $attributes .= ' ' . $attr . '="' . $value . '"';
            }
        }

        /**
         * No_Link_First_Child_Walker
         * Here I add a condition to check if depth is 1 so the tag will be h3
         * remove the <li> too for this depth
         */
        $output .= $indent . sprintf(
            (($depth == 1) ? '<h3 class="%s">%s%s%s</h3>' : '<li class="%s"><a%s>%s%s%s</a>'),
            $css_classes,
            $attributes,
            $args['link_before'],
            /** This filter is documented in wp-includes/post-template.php */
            apply_filters( 'the_title', $page->post_title, $page->ID ),
            $args['link_after']
        );

        if ( ! empty( $args['show_date'] ) ) {
            if ( 'modified' == $args['show_date'] ) {
                $time = $page->post_modified;
            } else {
                $time = $page->post_date;
            }

            $date_format = empty( $args['date_format'] ) ? '' : $args['date_format'];
            $output .= " " . mysql2date( $date_format, $time );
        }
    }

    public function end_el( &$output, $page, $depth = 0, $args = array() ) {
        if ( isset( $args['item_spacing'] ) && 'preserve' === $args['item_spacing'] ) {
            $t = "\t";
            $n = "\n";
        } else {
            $t = '';
            $n = '';
        }
        // No_Link_First_Child_Walker check depth and remove closing </li> for depth 1
        if($depth !== 1) {
            $output .= "</li>{$n}";
        }
    }

}