Use three queries to get data from the current post and next and previous posts in order to display Next and Previous post links.

Here's the code I use to add Next and Previous Post links to each blog post on this site. I've used this on a few sites and it's been described in different ways on the old Perch forum. But, I thought it would be useful to pull it together here.

Firstly, near the top of my page, we use perch_blog_custom to get the current post's data.

// get the post data, put it into $post variable
$post = perch_blog_custom([
  'filter'        => 'postSlug',
  'match'         => 'eq',
  'value'         => perch_get('s'),
  'skip-template' => true,
  'return-html'   => true
]);

// write the values from the array stored in $post to variables
  $date  = $post[0]['postDateTime'];
  $html   = $post['html'];

Now, I need to get the data from next and previous posts so that I can use this in the Next and Previous Links. I put this data into $next and $prev variables:

$prev = perch_blog_custom([
      'count'=>1,
      'filter'=>'postDateTime',
      'match'=>'lt',
      'sort'=>'postDateTime',
      'sort-order'=>'DESC',
      'value'=>$date,
      'template'=>'blog/post_prev.html'
        ], true); // stores prev post in a variable to use later
       
$next = perch_blog_custom([
      'count'=>1,
      'filter'=>'postDateTime',
      'match'=>'gt',
      'sort'=>'postDateTime',
      'sort-order'=>'ASC',
      'value'=>$date,
      'template'=>'blog/post_next.html'
      ], true); // stores next post in a variable to use later

The Next and Previous templates in the above are similar. Here's a simplified version of my blog/post_next.html template.

<li class="next">
    	<a href="/blog/<perch:blog id="postSlug" />" class="prev"><perch:blog id="postTitle" />
    	     	<time class='published' datetime="<perch:blog id="postDateTime" type="date" label="Date" time="true" format="Y-m-d H:i:s" />">
<perch:blog id="postDateTime" type="date" time="true" format="%d %B %Y" /></time> 
    	</a>
    </li>
</ul>

Finally, on my page, I can output the post and the Next and Previous Post links like this:

echo $html; // the post

// Previous and next post navigation
  if (empty($prev)){
          echo '<ul>';
    } else {
          echo $prev;
    }
  if (empty($next)){
      echo '</ul>';
    } else {
          echo $next;
  }

OK, that's it!

You should be able to see at least the Previous Post link below.