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I have a custom post type and a metabox with a file input.

I can insert the attachment, but I can't update the attachment metadata and I don't know how to fix it because I don't receive any error.

Here is my code:

$attach_id = wp_insert_attachment( $attachment, $filename, $post_id );
$attach_data = wp_generate_attachment_metadata( $attach_id, $filename );
wp_update_attachment_metadata( $attach_id,  $attach_data ); 

echo $attach_id;
echo '<pre>';
echo '</pre>';
echo '<pre>';
echo '</pre>';

and here is the output:

    [name] => one.png
    [type] => image/png
    [tmp_name] => /tmp/phphQ0e2v
    [error] => 0
    [size] => 144555

As you can see, $attach_data is empty :(

share|improve this question
Solved. I had to add $upload = wp_handle_upload($filename, array('test_form' => false)); and then pass "$upload['file']" to wp_insert_attachment and wp_update_attachment_metadata instead of $filename :) – Klian Apr 24 '12 at 17:20
Please add your solution as an answer and mark the question as answered. Thanks. – toscho Apr 25 '12 at 15:31
It is important to note that the first argument of wp_handle_upload is not a string but an array. So just passing the file-path won't work.. – hugo der hungrige Apr 10 '14 at 19:41

From comment:

Let WordPress generate a file path and use that for the next steps:

$upload    = wp_handle_upload($filename, array('test_form' => false));
$attach_id = wp_insert_attachment( $attachment, $upload['file'], $post_id );
wp_update_attachment_metadata( $attach_id,  $attach_data ); 
share|improve this answer

This is, what finally fixed it for me:

apply_filters('wp_handle_upload', array(
    'file' => $file_path, 
    'url' => $file_url, 
    'type' => $file_type), 

Explanation: I'm not quite sure why this fixed the error for me, but I assume that this either has something to do with plugins using the wp_handle_upload hook or that the filters add meta-data to the attachment, which otherwise would be missing in the wp_generate_attachment_metadata function.

Full function:

function add_to_media_lib($file_url, $file_path, $parent_post_id)
require_once(ABSPATH . 'wp-admin/includes/image.php');
require_once(ABSPATH . 'wp-admin/includes/file.php');

// Check the type of tile. We'll use this as the 'post_mime_type'.
$file_type = wp_check_filetype(basename($file_url), null);

// Get the path to the upload directory.
$wp_upload_dir = wp_upload_dir();

// Prepare an array of post data for the attachment.
$attachment = array(
    'guid' => $wp_upload_dir['url'] . '/' . basename($file_url),
    'post_mime_type' => $file_type['type'],
    'post_title' => preg_replace('/\.[^.]+$/', '', basename($file_url)),
    'post_content' => '',
    'post_status' => 'inherit',
    'post_parent' => $parent_post_id

// Insert the attachment.
$attach_id = wp_insert_attachment($attachment, $file_url, $parent_post_id);

// apply filters (important in some environments)
apply_filters('wp_handle_upload', array('file' => $file_path, 'url' => $file_url, 'type' => $file_type), 'upload');

// Generate the metadata for the attachment, and update the database record.
if ($attach_data = wp_generate_attachment_metadata($attach_id, $file_path)) {
    wp_update_attachment_metadata($attach_id, $attach_data);
} else {
    echo '<div id="message" class="error"><h1>Failed to create PDF-thumbnail Meta-Data</h1><pre>' . print_r($attach_data) . '</pre></div>';

return $attach_id;
share|improve this answer
Always add a short description to why your solution works, don't just add a lot of code and says it works. – Pieter Goosen Apr 10 '14 at 21:17

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