Uploaded attachment not set as featured image

Question

The following code uploads an image which I want to associate with a custom post type.

$upload_overrides = array( 'test_form' => FALSE );
if($file_errors['error'] == 0) {

  if($new_reseller_id = wp_insert_post( $new_reseller_profile_data )){

    //$this->wps_process_image($file, $new_reseller_id);exit;

    $uploaded_file = wp_handle_upload( $file, $upload_overrides );

    $wp_filetype = wp_check_filetype(basename($uploaded_file['file']), null );
    $wp_upload_dir = wp_upload_dir();
    $attachment = array(
      'guid' => $wp_upload_dir['url'] . '/' . basename( $uploaded_file['file'] ),
      'post_mime_type' => $wp_filetype['type'],
      'post_title' => preg_replace('/\.[^.]+$/', '', basename($file['name'])),
      'post_content' => '',
      'post_status' => 'inherit'
    );
    $attach_id = wp_insert_attachment( $attachment, $uploaded_file['file'], $new_reseller_id );
    // you must first include the image.php file
    // for the function wp_generate_attachment_metadata() to work
    $attach_data = wp_generate_attachment_metadata( $attach_id, $uploaded_file['file'] );
    wp_update_attachment_metadata( $attach_id, $attach_data );

  }
}

The image is uploaded and viewable in the image library but does not appear as the featured image in the custom post type editor. Why is this?

Answer 1

I needed to do the following:

set_post_thumbnail( $new_reseller_id, $attach_id );

Answer 2

You can also use update_post_meta

// Set Featured Image
update_post_meta($new_reseller_id, '_thumbnail_id', $attach_id);