get_body_class makes a raw, uncacheable query for child posts

[rmccue]

get_body_class() calls $wpdb->get_var( $wpdb->prepare("SELECT ID FROM $wpdb->posts WHERE post_parent = %d AND post_type = 'page' AND post_status = 'publish' LIMIT 1", $page_id) ) just so it can add a single class.

It also accesses the database directly this way, and is hence not cacheable at all, causing a query to be made on every page for something that's not always needed (but can't be disabled).

[obenland]

Is 28159.diff​ what we're looking for?

Before:

SELECT ID FROM wp_posts WHERE post_parent = 2 AND post_type = 'page' AND post_status = 'publish' LIMIT 1

After:

SELECT wp_posts.ID FROM wp_posts WHERE 1=1 AND wp_posts.post_parent = 2 AND wp_posts.post_type = 'page' AND ((wp_posts.post_status = 'publish')) ORDER BY wp_posts.post_date DESC LIMIT 0, 1

Introduced in r11053.

[kovshenin]

Using get_posts() will actually make it ​~ 5x slower and doesn't really do any useful caching.

[nacin]

This would work, and would leverage post caches:

$parent_page = get_post( $page_id );
if ( 'page' === $parent_page->post_type && 'publish' === $parent_page->post_status ) {

}

[kovshenin]

Replying to nacin: Sure, but that doesn't really give us the page's children. Perhaps "caching" the query result in a _wp_has_children meta and flushing it in wp_insert_post() could work?

[SergeyBiryukov]

How about get_pages()? It does use caching: tags/3.9.1/src/wp-includes/post.php#L4162​.

[kovshenin]

Replying to SergeyBiryukov: looks reasonable.

[SergeyBiryukov]

In 28696:

Use get_pages() instead of a raw SQL query in get_body_class().

fixes #28159.