Fix compatibility issues with The Event Calendar and Posts 2 Posts WordPress Plugins

tribe_p2p_compat_fix.php

<?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_20121001( $query ){
	if(isset($query->_p2p_capture) && $query->_p2p_capture) {
		add_filter( 'posts_fields', 'tribe_to_p2p_setupFields_20121001', 20);	
	} else {
		remove_filter( 'posts_fields', 'tribe_to_p2p_setupFields_20121001', 20);	
	}
	return $query;
}
function tribe_to_p2p_setupFields_20121001( $fields ){
	global $wpdb;
	$fields = "{$wpdb->posts}.ID";
	return $fields;
}
add_action( 'pre_get_posts', 'tribe_to_p2p_pre_get_posts_20121001');

I put this in my functions.php file after having issues with the many-to-many relationship in Posts 2 Posts connections when using Event Calendar and it worked like a charm.

Thanks for this! I found that I also needed to add:

$query->query_vars['eventDisplay'] = 'custom';

under the add_filter call.