posts of same category in next_posts_link

Read the docs:
Template_Tags/next_post_link – and its pair: previous…

Thanks for the hint. I looked at the link you provided and used this code

<?php if ( in_category('68'): ?>
	<div class="navigation">
		<div class="alignleft"><?php previous_post_link('&laquo; %link', 'previous', true) ?></div>
		<div class="alignright"><?php next_post_link('%link &raquo;', 'next', true) ?></div>
	</div>
<?php endif; ?>

and it works, but I still do not know how to have the prev/next links to order posts by title.. any ideas please?

how to have the prev/next links to order posts by title..

That sounds like a nonsense question.
You have ONE post before (a.k.a “previous”) and another ONE after (a.k.a. “next”) – in relation to the post that is viewed. What is there to be ordered?

When determining which post to use as next or previous post the call to next_post_link should order posts by title instead of default behaviour: by date of creation.

I found the answer to previous question, but now I am having problems implementing it. To change the ordering of posts in next_post_link I added a filter on ‘get_{$adjacent}_post_sort’ hook which is applied inside get_adjacent_post() when constructing the query.

relevant code from get_adjacent_post() in wp-includes/link-template.php

$adjacent = $previous ? 'previous' : 'next';
$op = $previous ? '<' : '>';
$order = $previous ? 'DESC' : 'ASC';

$join  = apply_filters( "get_{$adjacent}_post_join", $join, $in_same_cat, $excluded_categories );
$where = apply_filters( "get_{$adjacent}_post_where", $wpdb->prepare("WHERE p.post_date $op %s AND p.post_type = 'post' AND p.post_status = 'publish' $posts_in_ex_cats_sql", $current_post_date), $in_same_cat, $excluded_categories );
$sort  = apply_filters( "get_{$adjacent}_post_sort", "ORDER BY p.post_date $order LIMIT 1" );

return $wpdb->get_row("SELECT p.* FROM $wpdb->posts AS p $join $where $sort");

here is relevant plugin code: (WPD_print prints debuging messages to bottom of page. )

function filter_next_post_sort($sort) {
       $sort = "ORDER BY p.post_title ASC LIMIT 1";
	WPD_print('next sort: '.$sort);
	return $sort;
}

function filter_previous_post_sort($sort) {
       $sort = "ORDER BY p.post_title DESC LIMIT 1";
	WPD_print('previous sort: '.$sort);
        return $sort;
}

function filter_next_post_where($where) {
	WPD_print('next where: '.$where);
	return $where;
}

function filter_previous_post_where($where) {
   	WPD_print('previous where: '.$where);
	return $where;
}

add_filter('get_next_post_sort',   'filter_next_post_sort');
add_filter('get_next_post_where',  'filter_next_post_where');

add_filter('get_previous_post_sort',  'filter_previous_post_sort');
add_filter('get_previous_post_where', 'filter_previous_post_where');

filter_next_post_sort and filter_previous_post_sort replace ordering to use post_title. filter_next_post_where and filter_previous_post_where need to modify the where clause to remove post_date restrictions. For some reason I can’t get wordpress to call get_next_post_where and get_previous_post_where..

get_next_post_sort and get_previous_post_sort get called with no problems and filter functions get called and print debugging message.

never mind I found the problem.

never mind. I found the problem. thanks

great solution, thanks!

but Slavix, I must say that it would help a lot to paste the code correctly, you missed a ) in the first line…

Finally after a couple of days searching I discovered it and it works indeed splendid!

Cheers

I don’t see how the above code works. You modify the ORDER but not the WHERE … So for “next”, you are going to get the next alphabetical post that is newer, and for previous you will get the previous alphabetical post that is older.

Below is what I did to get it work:

function filter_next_post_sort($sort) {
  $sort = "ORDER BY p.post_title ASC LIMIT 1";
  return $sort;
}
function filter_next_post_where($where) {
  global $post, $wpdb;

  return $wpdb->prepare("WHERE p.post_title > '%s' AND p.post_type = 'post' AND p.post_status = 'publish'",$post->post_title);
}

function filter_previous_post_sort($sort) {
  $sort = "ORDER BY p.post_title DESC LIMIT 1";
  return $sort;
}
function filter_previous_post_where($where) {
  global $post, $wpdb;

  return $wpdb->prepare("WHERE p.post_title < '%s' AND p.post_type = 'post' AND p.post_status = 'publish'",$post->post_title);
}

add_filter('get_next_post_sort',   'filter_next_post_sort');
add_filter('get_next_post_where',  'filter_next_post_where');

add_filter('get_previous_post_sort',  'filter_previous_post_sort');
add_filter('get_previous_post_where', 'filter_previous_post_where');