SQL Errors from O2O_Connection_Taxonomy::get_connected_[*]_objects()

[emrikol]

Under the right conditions (or wrong conditions, depending on how you look at it), get_connected_[*]_objects() returns a WP_Error object that results in a SQL error:

Warning: implode(): Invalid arguments passed in /wp-includes/query.php on line 2658

WordPress database error You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ') AND wp_posts.post_type = 'post' AND (wp_posts.post_status = ' at line 1 for query SELECT wp_posts.ID FROM wp_posts WHERE 1=1 AND wp_posts.ID IN () AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private') ORDER BY wp_posts.post_date DESC LIMIT 0, 3 made by WP_Query::get_posts/

An example of how this can happen is if you want to set up a "related posts" section for the post post type in single.php:

...

add_action('init', 'o2o_related_posts');
function o2o_related_posts() {
    O2O::Register_Connection('o2o_related_posts', 'post', 'post', array(
        'reciprocal' => true,
        'to'         => array(

            'sortable' => true,
            'labels'   => array(

                'name'          => 'Related Posts',
                'singular_name' => 'Related Post'
            )
        ),
        'from'       => array(
            'labels' => array(
                'name'          => 'Posts',
                'singular_name' => 'Post'
            )
        )
    ) );
}

$o2o_query = new WP_Query( array(
    'o2o_query' => array(
        'connection' => 'o2o_related_posts',
        'id' => get_queried_object_id()
) ) );

...

If you don't check that 'post' !== get_post_type() then you will get the WP_Error object returned on all custom post type single posts.

One fix for this would be to just return an empty array() instead of the WP_Error object, but that doesn't address the need to notify the developer that they may be using the wrong post type (perhaps throw a PHP Warning or Notice?).