Get an attachment ID by URL in WordPress

We all know you can use wp_get_attachment_url() to return an attachment’s URL by passing in the ID, but what about the reverse scenario?

There are a lot of long-winded examples of how to get an attachment ID by URL floating around the interwebs. Most of them limit results to only returning images or use expensive DB queries. Really, there should be a function for this in core, but there isn’t.

Needless to say, I wasn’t really happy with any of the solutions I found people using, so I decided to take a stab at it.

Below is the most lightweight method I’ve come up with (so far) to get an attachment ID by passing through an attachment URL.

<?php
/**
 * Return an ID of an attachment by searching the database with the file URL.
 *
 * First checks to see if the $url is pointing to a file that exists in
 * the wp-content directory. If so, then we search the database for a
 * partial match consisting of the remaining path AFTER the wp-content
 * directory. Finally, if a match is found the attachment ID will be
 * returned.
 *
 * @param string $url The URL of the image (ex: http://mysite.com/wp-content/uploads/2013/05/test-image.jpg)
 * 
 * @return int|null $attachment Returns an attachment ID, or null if no attachment is found
 */
function fjarrett_get_attachment_id_by_url( $url ) {
	// Split the $url into two parts with the wp-content directory as the separator
	$parsed_url  = explode( parse_url( WP_CONTENT_URL, PHP_URL_PATH ), $url );

	// Get the host of the current site and the host of the $url, ignoring www
	$this_host = str_ireplace( 'www.', '', parse_url( home_url(), PHP_URL_HOST ) );
	$file_host = str_ireplace( 'www.', '', parse_url( $url, PHP_URL_HOST ) );

	// Return nothing if there aren't any $url parts or if the current host and $url host do not match
	if ( ! isset( $parsed_url[1] ) || empty( $parsed_url[1] ) || ( $this_host != $file_host ) ) {
		return;
	}

	// Now we're going to quickly search the DB for any attachment GUID with a partial path match
	// Example: /uploads/2013/05/test-image.jpg
	global $wpdb;

	$attachment = $wpdb->get_col( $wpdb->prepare( "SELECT ID FROM {$wpdb->prefix}posts WHERE guid RLIKE %s;", $parsed_url[1] ) );

	// Returns null if no attachment is found
	return $attachment[0];
}

Example usage

Just as an example, this would echo the attachment ID integer of test-image.jpg onto the page:

echo fjarrett_get_attachment_id_by_url( 'https://frankiejarrett.com/wp-content/uploads/2013/05/test-image.jpg' );

This would echo the same result as above because we are ignoring www usage in the URL being passed through:

echo fjarrett_get_attachment_id_by_url( 'https://frankiejarrett.com/wp-content/uploads/2013/05/test-image.jpg' );

This would echo nothing, because the image doesn’t exist in the WordPress uploads directory:

echo fjarrett_get_attachment_id_by_url( 'https://frankiejarrett.com/foo/test-image.jpg' );

And finally, this would also echo nothing because the URL of the file is pointing to an external domain:

echo fjarrett_get_attachment_id_by_url( 'http://www.anotherdomain.com/wp-content/uploads/2013/05/test-image.jpg' );

Conclusion

We managed to fetch an attachment ID in just a few lines of code with no expensive DB queries! Awesome 😎

Now you can do cool things like turn a URL into an absolute path:

$url = 'https://frankiejarrett.com/wp-content/uploads/2013/05/test-image.jpg';

$attachment_id = fjarrett_get_attachment_id_by_url( $url );

$path = ( $attachment_id ) ? get_attached_file( $attachment_id ) : null;

echo $path;

For more information about what was used in this function, please see:
http://php.net/manual/en/function.explode.php
http://php.net/manual/en/function.parse-url.php
http://php.net/manual/en/function.str-ireplace.php
http://codex.wordpress.org/Function_Reference/home_url
http://codex.wordpress.org/Determining_Plugin_and_Content_Directories#Constants
http://codex.wordpress.org/Class_Reference/wpdb#SELECT_a_Column

Was this code helpful to you? Let me know in the comments!