Filtering content with tags

Tags are a great way to separate your content into different categories and make it easier for your visitors to find the articles and pages they are looking for.

Adding Tags to your content

The perfect format to add tags to your content is a comma separated list.

Title: Some title
----
Text: Some great text
----
Tags: design, photography, architecture, whatever
----

Looks quite natural, right?

Filtering content by tag

The filterBy() method is built to make it possible to filter pages by a certain value in a field and even to filter pages by a certain value in a separated list like the tags list above. So we can use that to filter a set of pages by tag in a single line:

$filtered = $page->children()->filterBy('tags', 'design', ',');

This will search through all children of the current page and return all pages with the tag "design". The third argument of the method is telling it to search in a comma separated list. If you prefer to separate your tags with any other character you are free to do that and specify that separation character here.

In our blog.php template we fetched the latest articles like this:

$articles = $page->children()
                 ->visible()
                 ->flip()
                 ->paginate(10);

So if you want to filter them by a specific tag, go for:

$articles = $page->children()
                 ->visible()
                 ->filterBy('tags', 'design', ',')
                 ->flip()
                 ->paginate(10);

Controlling the filter by URL

At the end we want to be able to have different URLs for each tag filter. So something like http://yourdomain.com/blog/tag:fun should show all articles with tagged fun and http://yourdomain.com/blog/tag:design should show all design articles.

It's very easy to fetch those parameters passed by the URL with Kirby:

// url: http://yourdomain.com/blog/tag:design
echo param('tag');
// result: design

// url: http://yourdomain.com/blog/tag:fun
echo param('tag');
// result: fun

So what we need to do is to replace 'design' in our articles example above with the param function.

$articles = $page->children()
                 ->visible()
                 ->filterBy('tags', param('tag'), ',')
                 ->flip()
                 ->paginate(10);

Now you can filter all your articles in your blog by specifying the tag in the URL.

Of course we want to make sure that the filter is only applied when a tag is added to the URL. We need a little if clause to do that:


// fetch the basic set of articles
$articles = $page->children()->visible()->flip();

// add the tag filter
if($tag = param('tag')) {
  $articles = $articles->filterBy('tags', $tag, ',');
}

// apply pagination
$articles = $articles->paginate(10);

Tagcloud

To fetch all tags for a tagcloud you can use the new pluck method, which will extract a single field into an array.

<?php

// fetch all tags
$tags = $page->children()->visible()->pluck('tags', ',', true);

?>
<ul class="tags">
  <?php foreach($tags as $tag): ?>
  <li>
    <a href="<?php echo url('blog/' . url::paramsToString(['tag' => $tag])) ?>">
      <?php echo html($tag) ?>
    </a>
  </li>
  <?php endforeach ?>
</ul>

The url::paramsToString method will make sure that the resulting URL is compatible with both Linux and Windows servers.

Blog Controller

Putting it all together in /controllers/blog.php makes it easier to keep the blog template clean.

return function($site, $pages, $page) {

  // fetch the basic set of pages
  $articles = $page->children()->visible()->flip();

  // add the tag filter
  if($tag = param('tag')) {
    $articles = $articles->filterBy('tags', $tag, ',');
  }

  // fetch all tags
  $tags = $articles->pluck('tags', ',', false);

  // apply pagination
  $articles   = $articles->paginate(10);
  $pagination = $articles->pagination();

  return compact('articles', 'tags', 'tag', 'pagination');

};

The blog.php template has no logic in it afterwards, which makes it very simple and readable. The template will automatically have all the passed variables available ($articles, $pagination, $tags & $tag)

<?php snippet('header') ?>

<h1>Blog</h1>

<!-- articles -->
<?php foreach($articles as $article): ?>
<article>
  <h1><a href="<?php echo $article->url() ?>"><?php echo $article->title()->html() ?></a></h1>
  <?php echo $article->text()->excerpt(300) ?>
</article>
<?php endforeach ?>

<!-- sidebar with tagcloud -->
<aside>
  <h1>Tags</h1>
  <ul class="tags">
    <?php foreach($tags as $tag): ?>
    <li>
      <a href="<?php echo url($page->url() . '/' . url::paramsToString(['tag' => $tag])) ?>">
        <?php echo html($tag) ?>
      </a>
    </li>
    <?php endforeach ?>
  </ul>
</aside>

<!-- pagination -->
<nav class="pagination">
  <?php if($pagination->hasPrevPage()): ?>
  <a href="<?php echo $pagination->prevPageUrl() ?>">previous posts</a>
  <?php endif ?>

  <?php if($pagination->hasNextPage()): ?>
  <a href="<?php echo $pagination->nextPageUrl() ?>">next posts</a>
  <?php endif ?>
</nav>

<?php snippet('footer') ?>