get_adjacent_post() can generate invalid SQL

[dd32]

As reported on wp-testers, if get_adjacent_post() is used with $in_same_cat = true on a post type which does not support categories, then a invalid SQL will be generated.

eg:

SELECT p.* FROM wp_posts AS p INNER JOIN wp_term_relationships AS tr ON p.ID = tr.object_id INNER JOIN wp_term_taxonomy tt ON tr.term_taxonomy_id = tt.term_taxonomy_id AND tt.taxonomy = 'category' AND tt.term_id IN () WHERE p.post_date < '2010-07-04 12:24:53' AND p.post_type = 'note' AND p.post_status = 'publish' AND tt.taxonomy = 'category' ORDER BY p.post_date DESC LIMIT 1

specifically

AND tt.term_id IN ()

Whilst this is not a problem in the 2011 theme, Some themes may call the functions which can result in this.

wp-testers thread: ​http://lists.automattic.com/pipermail/wp-testers/2010-December/013841.html

one potential solution would be:

	// Check to see if the Post Type supports categories before honoring the argument.
	if ( $in_same_cat ) {
		$taxonomies = get_object_taxonomies($post);
		if ( ! in_array('category', $taxonomies) )
			$in_same_cat = false;
	}

From what I can see, this would not be a regression from any previous version of WordPress

[dd32]

Just confirming this was an issue in 3.0 as well.

[SergeyBiryukov]

Made a patch from Dion's proposed solution.

[dd32]

Related, but unrelated to the problem at hand - #13096 - use a custom taxonomy in place of category

[wpdavis]

Just updated the patch. Simply check if the array of object terms is empty.

[markauk]

This bug also manifests on post types which do support categories, but where no categories are set for a given post. Present in 3.2(18084).

Alternate patch attached which fixes both cases.

[scribu]

Related: #17807

[SergeyBiryukov]

Closed #20682 as a duplicate.

[westi]

This is pretty lame, we should fix it.

[batmoo]

Patch should catch scenarios where category taxonomy doesn't exist, post_type doesn't support the category taxonomy, and if post doesn't have any categories. We should return empty in all of these cases as we should honour the $in_same_cat request.

[nacin]

#22360 was marked as a duplicate.

[nacin]

Slightly tweaked patch on #22360 — use of is_object_in_taxonomy() rather than the WP_Error check, I guess.

[nacin]

This seems like a good thing to fix. There have been quite a few bug reports and no one likes a database error. westi, can you finish this off for 3.5?

[SergeyBiryukov]

The patch from #22360

[nacin]

In 22472:

Return nothing in get_adjacent_post() when $in_same_cat = true but the post doesn't support (or otherwise have) categories. Avoids SQL error. props batmoo, SergeyBiryukov. fixes #15959.