update_post_meta: data gets overwritten when uploading a file

Hi there,

Currently, I am working on a system that makes it more user friendly for customers to associate meta data with their posts using WordPress’s custom fields feature. It’s a bit like this, except I’m building a small object-oriented system for easier customization and extension.

Basically, the system now works. I can enter my custom metadata, it gets saved and displayed properly. However, a very weird problem appears when doing a file upload.

I want to give the customer the opportunity to add a thumbnail to a post using a file upload form. The code that gets invoked when a file is uploaded looks somewhat like this:

if(!empty($_FILES[$this->ikey.'_attach']['name']))
		{
			$upload = wp_handle_upload($_FILES[$this->ikey.'_attach'], array('action' => 'editpost'));
			$this->data = $upload['url'];
			return true;
		}

After which what’s now stored in $this->data gets saved using update_post_meta. The file gets uploaded allright, and I verified the contents of $upload which are perfectly in order. However, it appears a blank meta value is written to the database. The really strange thing here is that the code works perfectly for all possible values of $this->data, except for $upload[‘url’]; For example, if I change it to this:

if(!empty($_FILES[$this->ikey.'_attach']['name']))
		{
			$upload = wp_handle_upload($_FILES[$this->ikey.'_attach'], array('action' => 'editpost'));
			$this->data = 'Some random crap';
			return true;
		}

then the value ‘Some random crap’ gets written to the database. I find this behaviour very strange, so I took a look at my MySQL logs. I can actually see the meta value being updated to the right URL, after which its get updated again… to an empty string. This only happens when I assign $upload[‘url’] to $this->data. In all other cases the system works perfectly fine, even when I manually enter an URL that’s the same as what $upload[‘url’] is going to be!

So, this problem’s got me stumped for a couple of hours now and I didn’t come any closer to a solution. If anyone knows why WordPress is overwriting my URL with an empty string, I’d be very thankful!

– Jurre