Allow selection of a post type on media attachments in WordPress

jdp-attachment-fields.php

<?php
/**
* Add Photographer selection to media upload
*
* @param $form_fields array, fields to include in attachment form
* @param $post object, attachment record in database
* @return $form_fields, modified form fields
*/
function bsj_attachment_field_credit( $form_fields, $post ) {
	//do_dump($post);
	
	$form_fields['jdp_photographer'] = array(
		'label' => 'Contributor:',
		'input' => 'html',
		'helps' => 'Choose the photographer/artist for this image',
	);
	
	//GET THE CURRENT PHOTOGRAPHER
	$current_photog = get_post_meta($post->ID, 'jdp_photographer', true);
	//do_dump($current_photog);
	if ( !isset($current_photog) ) {
		$current_photog = 0;	
	}
	
	//SETUP THE FORM FIELD
	$form_fields['jdp_photographer']['html'] = '<select name="attachments['.$post->ID.'][jdp_photographer]" id="attachments['.$post->ID.'][jdp_photographer]">';
	
	//OUTPUT NULL FIELD
	$form_fields['jdp_photographer']['html'] .= '<option value="0" '.selected(0, $current_photog, false).'>Choose one...</option>';
	
	//GET THE TERMS IN THE 'jdp_contributor_types' taxonomy, excluding authors
	$terms = get_terms( 'jdp_contributor_types', array('fields' => 'ids', 'hide_empty' => false, 'exclude' => '32') );
	
	//GET THE PHOTOGRAPHERS
	$args = array(
		'post_type' => 'jdp_contributors',
		'nopaging' => true,
		'posts_per_page' => -1,
		'tax_query' => array(
			array(
				'taxonomy' => 'jdp_contributor_types',
				'field' => 'id',
				'terms' => $terms
			),
		),
		'orderby' => 'name',
		'order' => 'ASC',
	);
	$photographers = new WP_QUERY($args);
	do_dump($photographers);
	
	//LOOP THRU THE PHOTOGRAPHERS
	foreach( $photographers as $postdata ) {
		setup_postdata($postdata);
		$form_fields['jdp_photographer']['html'] .= '<option value="'.$postdata->ID.'" '.selected($postdata->ID, $current_photog, false).'>'.$postdata->post_title.'</option>';
	}
	wp_reset_query();
	
	$form_fields['jdp_photographer']['html'] .= '</select>';
	
	return $form_fields;
}
add_filter( 'attachment_fields_to_edit', 'bsj_attachment_field_credit', 10, 2 );


/**
* Save values of Photographer Name and URL in media uploader
*
* @param $post array, the post data for database
* @param $attachment array, attachment fields from $_POST form
* @return $post array, modified post data
*/
function jdp_attachment_field_credit_save( $post, $attachment ) {
	if (isset( $attachment['jdp_photographer'] ) )
		update_post_meta( $post['ID'], 'jdp_photographer', $attachment['jdp_photographer'] );
	
	return $post;
}
add_filter( 'attachment_fields_to_save', 'jdp_attachment_field_credit_save', 10, 2 );
?>