wordpress where clause overwrite to query on custom field

functions.php

<?php
// If on events page get only upcoming events.
if (segments(2) === 'events' AND ! is_single())
{
    
    // Our query overwrite. Fancy, hacky, wonderful.
    function filter_where($where = '') 
    {
        global $wpdb;
    	$now = strtotime('now'); // Get current timestamp.
    	// Overwrite entire where clause to get the upcoming events.
    	$where = "AND wp_posts.post_type = 'events' AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private')".
    	" AND wp_postmeta.meta_key = 'date_of_event' AND UNIX_TIMESTAMP(wp_postmeta.meta_value) >= $now";
    	return $where;
    }
    
    // Add the where filter.
    add_filter('posts_where', 'filter_where');
    
    // Preform query.
    query_posts(array(
        'post_type'  => 'events',
        'order'      => 'ASC',
        'paged'      => get_query_var( 'paged' ) ? get_query_var( 'paged' ) : 1,
        
        // Need to add this so query_posts joins the postmeta table in the query. 
        // Above I overwrite the where bit and use meta. Via filter_where()
        'meta_query' => array(array('key' => '','value' => '','compare' => '','type' => ''))
    ));
    
    // Remove the filter.
    remove_filter('posts_where', 'filter_where'); 
}