Unexpected conflict with custom queries

[codearachnid]

I ran into an interesting DB error:

WordPress database error: [Operand should contain 1 column(s)]

upon further review it turns out that the bug was being created by another plugin, Tri.be's The Event Calendar (side note: which I'm a dev for). We are doing a major overhaul of our plugin's query structure that will fix this issue down the line. In the interest of suggesting a clean way to prevent this from happening to older versions of our plugin or other plugins that might be cluttering WP_Query with custom fields, I submit this simple filter to ensure the nested select only has 1 column.

<?php

/**
 * Fix compatibility issues with The Event Calendar and Posts 2 Posts WordPress Plugins
 * Issue arrises with how nested select queries function when P2P expects a single column.
 */

function tribe_to_p2p_pre_get_posts( $query ){
    if(isset($query->_p2p_capture) && $query->_p2p_capture) {
        add_filter( 'posts_fields', 'tribe_to_p2p_setupFields', 20);    
    } else {
        remove_filter( 'posts_fields', 'tribe_to_p2p_setupFields', 20); 
    }
    return $query;
}
function tribe_to_p2p_setupFields( $fields ){
    global $wpdb;
    $fields = "{$wpdb->posts}.ID";
    return $fields;
}
add_action( 'pre_get_posts', 'tribe_to_p2p_pre_get_posts');

Source: https://gist.github.com/3815849

[sstasio]

Thanks for this solution, it was driving me crazy trying to figure this out.

[codearachnid]

Glad it was able to help you out.