Rocking a portfolio custom post type with Previous / Next links? Want a Next link on the last portfolio page to simply link back to the first? Ha! Have fun with that. Turns out, that's not so easy huh? Wp's <?php previous_post(); ?> tag doesn't work like that out the box. So, just throw this puppy into your functions.php and use the created <?ph…

Wordpress Circular Nav for Single Post Types

/*===================================================================================
Circular Navigation for Single CPT files (or just your single.php)
From: 
http://wordpress.org/plugins/loop-post-navigation-links/

Example Useage:
For use with next / last post markup that would look a little something like this:
<div id="folio-nav">
  <div class="prev-post">
	  <?php themename_previous_or_loop_post_link( '%link', '<span class="icon-left"></span>'); ?>
  </div>
  <div class="next-post"> 
	  <?php themename_next_or_loop_post_link( '%link', '<span class="icon-right"></span>'); ?>
  </div>
</div>
===================================================================================*/

defined( 'ABSPATH' ) or die();

global $themename_loop_navigation_find;
$themename_loop_navigation_find = false;

//themename_next_or_loop_post_link function
if ( ! function_exists( 'themename_next_or_loop_post_link' ) ) :

function themename_next_or_loop_post_link( $format='%link &raquo;', $link='%title', $in_same_cat = false, $excluded_categories = '' ) {
	themename_adjacent_or_loop_post_link( $format, $link, $in_same_cat, $excluded_categories, false );
}
add_action( 'themename_next_or_loop_post_link', 'themename_next_or_loop_post_link', 10, 4 );
endif;

if ( ! function_exists( 'themename_previous_or_loop_post_link' ) ) :

// Display previous post link that's next door to current post. If none, then hows about the last post in series.
function themename_previous_or_loop_post_link( $format='&laquo; %link', $link='%title', $in_same_cat = false, $excluded_categories = '' ) {
	themename_adjacent_or_loop_post_link( $format, $link, $in_same_cat, $excluded_categories, true );
}
add_action( 'themename_previous_or_loop_post_link', 'themename_previous_or_loop_post_link', 10, 4 );
endif;

if ( ! function_exists( 'themename_adjacent_or_loop_post_link' ) ) :

//Display adjacent post link or the post link for the post at the opposite end of the series.
function themename_adjacent_or_loop_post_link( $format, $link, $in_same_cat = false, $excluded_categories = '', $previous = true ) {
	if ( $previous && is_attachment() && is_object( $GLOBALS['post'] ) )
		$post = get_post( $GLOBALS['post']->post_parent );
	else
		$post = get_adjacent_post( $in_same_cat, $excluded_categories, $previous );

	// START The only modification of adjacent_post_link() -- get the last/first post if there isn't a legitimate previous/next post
	if ( ! $post ) {
		global $themename_loop_navigation_find;
		$themename_loop_navigation_find = true;
		$post = get_adjacent_post( $in_same_cat, $excluded_categories, $previous );
		$themename_loop_navigation_find = false;
	}
	// END modification

	if ( ! $post ) {
		$output = '';
	} else {
		$title = $post->post_title;

		if ( empty( $post->post_title ) )
			$title = $previous ? __( 'Previous Post' ) : __( 'Next Post' );

		$title = apply_filters( 'the_title', $title, $post->ID );
		$date = mysql2date( get_option( 'date_format' ), $post->post_date );
		$rel = $previous ? 'prev' : 'next';

		$string = '<a href="' . get_permalink( $post ) . '" rel="' . $rel . '">';
		$link = str_replace( '%title', $title, $link );
		$link = str_replace( '%date', $date, $link );
		$link = $string . $link . '</a>';

		$output = str_replace( '%link', $link, $format );
	}

	$adjacent = $previous ? 'previous' : 'next';

	// Apply the filters present in WP's adjacent_or_loop_post_link()
	$output = apply_filters( "{$adjacent}_post_link", $output, $format, $link, $post );

	// Apply old {$adjacent}_or_loop_post_link filters.
	// Deprecated as of v2.0. Here temporarily for backwards compatibility.
	$output = apply_filters( "{$adjacent}_or_loop_post_link", $output, $format, $link, $post );

	// Apply custom filters and echo
	echo apply_filters( "themename_{$adjacent}_or_loop_post_link_output", $output, $format, $link, $post );
}
add_action( 'themename_adjacent_or_loop_post_link', 'themename_previous_or_loop_post_link', 10, 5 );
endif;

if ( ! function_exists( 'themename_modify_nextprevious_post_where' ) ) :

// Modifies the SQL WHERE clause used by WordPress when getting a previous/next post to accommodate looping navigation.
//Can be either next post link or previous.
function themename_modify_nextprevious_post_where( $where ) {
	// The incoming WHERE statement generated by WordPress is a condition for the date, relative to the current
	//	post's date.  To find the post we want, we just need to get rid of that condition (which is the first) and retain the others.
	if ( $GLOBALS['themename_loop_navigation_find'] )
		$where = preg_replace( '/WHERE (.+) AND/imsU', 'WHERE', $where );
	return $where;
}
endif;

//Register actions to filter WHERE clause when previous or next post query is being processed.
add_filter( 'get_next_post_where',     'themename_modify_nextprevious_post_where' );
add_filter( 'get_previous_post_where', 'themename_modify_nextprevious_post_where' );