P2P Admin Dropdown

gistfile1.php

# author: sdls
# source: http://wordpress.org/support/topic/p2p-admin-view-sort-by-drop-down#post-3446538

function restrict_posts_by_relation() {
		global $typenow;
		$post_type = 'yourfirstposttype'; // change HERE
		$related_post = 'yoursecondposttype'; // change HERE
		$related_post_drop_down = 'related_'. $related_post. '_post';

		if ($typenow == $post_type) {
			// $selected = isset($_GET[$related_post]) ? $_GET[$related_post] : '';

			// create the drop down of related posts

			$args = array(
			'orderby'=>'title',
			'order'    => 'ASC',
			'showposts' => '-1',
			'post_type' => $related_post,
			);
			$dropposts = new WP_Query($args);
			if( $dropposts->have_posts() ):
			?>
				<select id="<?php echo $related_post_drop_down; ?>" class="postform" name="<?php echo $related_post_drop_down; ?>">
					<?php
					while( $dropposts->have_posts() ): $dropposts->the_post();
					// setup_postdata($post);
					?>
					<option class="level-1" value="<?php the_ID(); ?>"><?php the_title(); ?></option>
					<?php
					endwhile;
					?>
				</select>
				<?php
			endif;
			wp_reset_postdata();

		};
	}

	add_action('restrict_manage_posts', 'restrict_posts_by_relation');

	function convert_relation_to_query($query) {
		global $pagenow;
		$post_type = 'yourfirstposttype'; // change HERE
		$related_post = 'yoursecondposttype'; // change HERE
		$related_post_drop_down = 'related_'. $related_post. '_post';
		$connection_reference = 'youronnectionreference';
// change HERE
		$related_post_ID = $_GET[$related_post_drop_down];

		$q_vars = &$query->query_vars;

		if ($pagenow == 'edit.php' && isset($q_vars['post_type']) && $q_vars['post_type'] == $post_type && isset($related_post_ID) && is_numeric($related_post_ID) && $related_post_ID != 0) {

		// echo "beep";
			$mod_post = get_post( $related_post_ID );
			// print_r($mod_post);
			$args = array(
			  'connected_type' => $connection_reference,
			  'connected_items' => $mod_post,
			);
			query_posts($args);

		}
	}

	add_filter('parse_query', 'convert_relation_to_query');