How to set up WP Cron in this scenario

Question

I wanted to use Wordpress built in WP Cron to update currency rates daily.

I use this function currently,

require_once(WP_PLUGIN_DIR . '/autocurupdate/currencyexchange_class.php');
$cx=new currencyExchange();
$cx->getData();
$currency_sql = "select last_updated from " . $wpdb->prefix."currencies where code = 'PHP'";
$currency_1 = mysql_query($currency_sql);
$currency_2 = mysql_fetch_array($currency_1);
$last_updated = mysql2date(get_option('date_format'), $currency_2['last_updated']);
$current_date = $cx->Date;
$currentdate = mysql2date(get_option('date_format'), $current_date);
if($last_updated !== $currentdate) {
update_currency();
}

How can I run update_currency() function daily using WP Cron?

Answer 1

First things first: Say hello! to $wpdb

The wpdb Class is what you take to interact with the database on it's most basic level. Forget all those mysql_* functions, when it comes to WordPress. The core has a nice wrapper, that makes most things pretty safe for you (hint: SQL-injections and other bad boys). Or at least offers things, that you can use to make it safe (like_escape(), $wpdb->prepare() to mention some).

---

The Schedule API

WordPress comes with some sort of pseudo Cron Job:

• Schedule API It's not that well documented, but this is what comes a real Cron Job closest. Make sure, that you read everything about it and try it in a clean install.

I have written a small plugin, that will allow you inspect what you're doing. It's called »WP Cron Jobs List« and is hosted on GitHub/Gist or via our own WPSE Plugin repository.