get_pages filter may be applied twice

[DD32]

This is a bit hard to explain; so hang in there while reading.

Under certain conditions(WP Object cache being enabled), the get_pages filter is applied twice:

First, We get the pages from the database, And filter it.

$pages = $wpdb->get_results($query);
	$pages = apply_filters('get_pages', $pages, $r);

Thats fine, Next, We locate any children, and cache it:

if ( $child_of || $hierarchical )
		$pages = & get_page_children($child_of, $pages);

	$cache[ $key ] = $pages;
	wp_cache_set( 'get_pages', $cache, 'page' );

Thats also fine, So we've got the results, we've filtered it, and now we've put it into the cache as filtered.

Now, Next time the function runs:

	$key = md5( serialize( $r ) );
	if ( $cache = wp_cache_get( 'get_pages', 'page' ) )
		if ( isset( $cache[ $key ] ) )
			return apply_filters('get_pages', $cache[ $key ], $r );

We pull the cached _filtered_ results, and then we filter it again.

In general this isnt an issue, But if you've got a plugin adding pages to the get_pages function, AND the cache is enabled, then it ends up that the page will be added twice, Once when pulling from the DB, And then it'll be added again when its pulled from the cache later.

I've attached a patch to remove the filtering upon a cache retrieval, This has the downside that any plugin which modifies the get_pages output will have to deal with its output being cached.

I've also attached a patch to update the cache before filtering, So the filtering allways takes place.

[DD32]

delay the fitlering until after caching

[DD32]

remove the get_pages filter on the cached result

[DD32]

There was an error in the "4712.remove_cached_filter.diff" patch, replaced with .2

[markjaquith]

I've also attached a patch to update the cache before filtering, So the filtering allways takes place.

That sounds like the most flexible solution with least chance of breakage.

(FYI: I deleted your old patch)

[markjaquith]

(In [5855]) Avoid running get_posts filter twice. Props DD32. fixes #4712

[epper]

If you have a plugin adding pages to the get_pages() function by the 'get_pages' filter AND the get_pages() function itself doesn't find any page, the result should infact be only the pages added by the plugin via the filter.

The problem is that with the change discussed in this ticket (and now live in wordpress 2.3) this cannot appen because of these lines: (in wp 2.2 this was ok)

1187 	    if ( empty($pages) )
1188 	        return array();

On empty result set from the database, the empty result is returned and is not filtered.

I don't really know wordpress code like you all but I think that this simple patch could help to solve the problem:

1187 	    if ( empty($pages) )
1188 	        return apply_filters('get_pages',array(),$r);

With this change, my plugin, which allows to add private pages (with a special parameter) to the wp_list_pages output, now works correctly.

[ryan]

(In [6204]) Apply filteres when returning empty array from get_pages. Props epper. fixes #4712 for trunk

[ryan]

(In [6205]) Apply filteres when returning empty array from get_pages. Props epper. fixes #4712 for 2.3