Page Classes - Diving into one of ProcessWire's best features

[FireWire]

Page classes are an outstanding feature of ProcessWire and probably ranks among my favorites overall (and that's really saying something with ProcessWire). I don't remember how I lived without them, well I do, but I don't like to think about it.

I wrote a response to a question asking how ProcessWire can help transition from procedural code to OOP and in the process (pardon the pun) of answering, I realized how much I've come to use, if not outright rely on, page classes in every project. I wanted to compile a few more thoughts and examples here because there may be devs who are finding this feature for the first time, and besides, why not go down the rabbit hole?

Page classes have been around since ProcessWire 3.0.152 and if you're not familiar this will all make a lot more sense if you do a quick read of the feature announcement by Ryan here because this post assumes familiarity. We're also going to pick up the pace between the examples below compared to my comment in the link above.

Here are a few goals that I have that page classes put solutions for within reach. You may have some of your own and I'd love to hear about those as well.

• Keep templates clean by restricting logic to flow operations- if statements and loops.
• Work with data in context, accessing data and fields closer to their source.
• Create "universal" methods available in every template, but also have scoped methods per-template
• Increase the scalability of a project, growth with limited increases in complexity.
• Stay DRY
• Embrace and extend the power of OOP in ProcessWire's DNA

This seems like quite a list for one feature to handle, but rest assured, this is an example of how much power comes with using page classes. I'll continue and build on the blog example from my linked response above, and you can "follow along" with the Blog module since the templates mentioned are present out of the box. Some of the examples below are taken from production code, but please excuse any errors that I may have introduced by accident and I'm happy to update this post with corrections. Some of these things can be done other ways but they're just to illustrate, replace with your ideas and think of times that this would be useful.

First up, what are some features and behaviors that everyone needs on every project? What are some universal methods that would be great to have everywhere? Let's start out by creating a "base" page class. Going forward, page classes will extend this class instead of Page and benefit from having access to universal methods and properties. Make sure you pick a name that won't collide with a template name, we'll assume there's no plans for a base.php template.

<?php namespace ProcessWire;

// /site/classes/BasePage.php

class BasePage extends Page {

  /**
   * Returns all top level pages for the main navigation.
   */
  public function navigationPages(): PageArray {
    $pages = wire('pages');
    $selector = 'parent=1';
    $excludedIds = $pages->get('template=website_settings')
      ->nav_main_excluded_pages
      ->explode('id');

    // Check for excluded pages from nav defined in the "Website Settings" page
    count($excludedIds) && $selector .= ',id!=' . implode('|', $excludedIds);

    $homePage = $pages->get('id=1');
    $topLevelPages = $pages->find($selector);
    $topLevelPages->prepend($homePage);

    return $topLevelPages;
  }

}

All your base page are belong to us. Right off the bat we've managed to pull complex logic usually in templates and kept our markup clean. This isn't for DRY, it's to store logic out of templates.  This simple example only illustrates working with a top level page nav. We can start to appreciate the simplicity when considering how much more the navigation may call for in the future. A navigationChildren method that also accounts for excluded pages is a prime example. In our markup:

<!-- /site/templates/components/site_nav.php -->
<nav>
  <ul>
    <?php foreach ($page->navigationPages() as $navPage): ?>
      <li>
        <a href="<?= $navPage->url; ?>"><?= $navPage->title; ?></a>
      </li>
    <?php endforeach ?>
  </ul>
</nav>

Next up, our settings page has newsletter signup fields where users can copy/paste form embed code from Mailchimp.

• Our website has a "settings" page where global values and fields can be edited and maintained
• There are multiple textarea fields on the settings page that can each contain a different mailchimp embed code
• There is an embed select field that can be added to templates. The values are textarea field names so an embed can be chosen by the user.
• An embed select field has been added to the settings page which allows for choosing a default embed code if one isn't selected when editing a page
• Embedded forms should be available anywhere on any template

<?php namespace ProcessWire;

// /site/classes/BasePage.php

class BasePage extends Page {

  // ...Other BasePage methods

  /**
   * Renders either a selected form embed, fallback to default selected form
   */
  public function renderEmailSignup(): ?string {
    $settingsPage = wire('pages')->get('website_settings');
    
    $embedField = $this->signup_embed_select ?: $settingsPage->default_email_embed;

    return $settingsPage->$embedField;
  }

}

Excellent. We've got some solid logic that otherwise wouldn't have a great home to live in without page classes. We can also modify this one method if there are additional options or complexity added to the admin pages in the future. Wherever we use renderEmailSignup, the return value will be either the selected or default form embed code.

Let's create a folder called "components" in our templates directory that will hold standalone reusable markup we can use wherever needed, here's our newsletter signup component:

 <!-- /site/templates/components/newsletter_signup.php -->
<div class="newsletter-signup">
  <?= $page->renderEmailSignup(); ?>
</div>

Great! We've kept logic out of our code. We can render the field, and we can account for an empty value with a fallback. Unfortunately this is pretty limited in that it only handles a specific field, and it's implementation isn't as flexible as a component should be.

We can fix that, and here are some new requirements to boot:

• Some templates may have multiple embed select fields which may or may not have a value
• Each embed select field is now paired up with a text field to add some content that appears with each form embed, think "Sign up for our newsletter today!"
• We want to render our mailchimp form embeds using the same component file, but handle different fields

Sounds like a tall order, but it's a challenge easily overcome with page classes. We're going to introduce a new method called renderComponent that will be global, reusable, and very flexible. We're also going to make use of another very great ProcessWire feature to do it. Back to our BasePage class:

<?php namespace ProcessWire;

// /site/classes/BasePage.php

class BasePage extends Page {

  // ...Other BasePage methods

  /**
   * Renders a file located in /site/templates/components/ with optional variables
   */
  final public function renderComponent(string $file, ...$variables): string {
    $componentsPath = wire('config')->paths->templates . 'components/';

    return wire('files')->render($file, $variables, ['defaultPath' => $componentsPath]);
  }

  /**
   * Renders either a selected form embed, fallback to default selected form
   */
  public function renderEmailSignup(?string $embedSelectField = null): ?string {
    $settingsPage = wire('pages')->get('website_settings');
    
    $embedField = $this->$embedSelectField ?: $settingsPage->default_email_embed;

    return $settingsPage->$embedField;
  }

}

We've done a couple of things here. We've updated renderEmailSignup to accept a field name, so now we're flexible on exactly which field select we'd like to check for a value on before falling back to default. We've also created a renderComponent method that is going to be super useful throughout the rest of our ProcessWire application.

Our renderComponent receives a file name located in the components directory and any number of named parameters. You could change the $variables parameter to an array if you'd like, but I'm a big fan of the great features we have now in PHP 8+. Here's our refactored component file:

 <!-- /site/templates/components/newsletter_signup.php -->
 <?php if ($embedField): ?>

  <div class="newsletter-signup">
    <?php if ($text): ?>
      <h2><?= $text; ?></h2>
    <?php endif ?>

    <?= $page->renderEmailSignup($embedField); ?>
  </div>
 
 <?php endif ?>

And let's hop over to our (abbreviated) home page template:

<body>
  <!-- ...Sections full of great content -->

  <section class="signup-call-to-action">
    <?= $page->renderComponent('newsletter_signup.php', embedField: $page->embed_select, text: $page->text_1); ?>
  </section>

  <!-- ...Your awesome template design -->

  <section class="page-end-call-to-action">
    <?= $page->renderComponent('newsletter_signup.php', embedField: $page->embed_select_2, text: $page->text_2); ?>
  </section>

  <!-- Your footer here -->
</body>

I don't know about you, but this is looking really good to me. The number of things we've accomplished while having written so little code is remarkable:

• Because we used wire('files')->render(), the entire ProcessWire API is available within the component, so now our renderEmailSignup method is too.
• The variadic function parameters (or array if preferred) let us pass an arbitrary number of variables to any component file, unrestricted future flexibility
• Variables are scoped to each component! There's no reference to template fields in our component that could break if changes are made
• No more PHP includes, we don't have to juggle paths or constantly repeat them in our code, nor rely on declaring variables before including a file.
• ProcessWire will throw an exception if we try to render a file that does not exist which makes locating issues very easy
• We'll also see an exception if we try to reference a variable in our component that wasn't passed which can also help troubleshooting.
• Notice that the renderComponent is final. We want that behavior to remain consistent everywhere we use it and not overwritten either intentionally or by accident on our inheriting page classes. We want to eliminate any confusion between templates by knowing it will always do the same thing the same way.

We can explore other uses too, perhaps a renderPartial for files in /site/templates/partials where we store files like site_header.php.  As mentioned above however, if a variable is expected in the rendered file but not included in our render method, we'll see an exception. Let's use site_header.php as an example because we're sure to run into situations where variables may or may not exist:

<?php namespace ProcessWire;
// /site/templates/partials/site_header.php
?>
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title><?= $page->title; ?></title>
  <meta name="description" content="<?= $metaDescription ?? null; ?>">
  <?php if ($includeAnalytics ?? true): ?>
    <script>
      // All that Google Analytics jazz
    </script>
  <?php endif ?>
</head>
<body class="<?= $bodyClasses ?? null; ?>">
  <header>
    <?= $page->renderComponent('site_nav.php', includeEmailButton: true); ?>
  </header>

Problem: solved. By using nullsafe ?? operators, we can call $page->renderPartial('site_header', description: 'The ultimate Spice Girls fan page.'); and never get errors for variables that may not be included when calling renderComponent, such as includeAnalytics, which now also has a default value of 'true'. Nice.

We haven't even gotten to our actual page classes yet... Our templates are about to receive superpowers.

Let's take our blog to the next level. In my comment on the other thread, I created a specific example of adding a readTime method to our blog posts, let's go one level higher to our blog.php template. We'll populate some methods up front and then talk about what we've done:

<?php namespace ProcessWire;

// /site/classes/BlogPage.php

class BlogPage extends BasePage {

  /**
   * Get latest blog posts, optionally with/without pinned post, optionally in blog category
   */
  public function latestPosts(
    int $limit = 3,
    bool $includePinnedPost = true,
    ?int $categoryId = null
  ): PageArray {
    $selector = 'template=blog-post';

    if ($categoryId) {
      $selector .= ",blog_category={$categoryId}";
    }

    $posts = wire('pages')->get($selector);

    if ($includePinnedPost) {
      $pinnedPost = $this->getPinnedPost();

      if ($pinnedPost) {
        $posts->remove($pinnedPost);
        $posts->prepend($pinnedPost);
      }
    }

    return $posts->slice(0, $limit);
  }

  /**
   * Gets an optional pinned post if set/chosen
   * pin_blog_post A checkbox to indicate whether a post should be pinned
   * pinned_post   A InputfieldPage field to choose a blog post
   */
  public function getPinnedPost(): ?Page {
    if (!$this->pin_blog_post) {
      return null;
    }

    return wire('pages')->get($this->pinned_post);
  }

}

On our main blog page a user has the ability to choose whether a blog post is "pinned". A pinned post will always remain the first post anywhere a list of posts is needed, something like a big company announcement that the client wants to keep visible. These two methods alone have given us awesome abilities.

For our main blog page, when someone visits our blog page, the most recent or pinned post is presented at the top, followed by the next two most recent posts, followed by two rows of 3 posts, for a total of 9. Let's assume that we've already created the BlogPostPage.php with the readTime method from my previous example. Here's our blog.php template

<?php namespace ProcessWire;

echo $page->renderPartial(
  'site_header.php',
  bodyClasses: 'blog-page',
  metaDescription: $page->blog_description
);

$posts = $page->latestPosts(9);
$firstPost = $blogPosts->first();
?>

<section class="main-post">
  <article>
  	<img src="<?= $firstPost->blog_image->url; ?>" alt="<?= $firstPost->blog_image->description; ?>">
  	<h1><?= $firstPost->title; ?></h1>
  	<?= $firstPost->summary; ?>
  	<span><?= $firstPost->readTime(); ?></span>
  	<a href="<?= $firstPost->url; ?>">Read More</a>
  </article>
</section>

<section class="recent-Posts">
  <?= $page->renderComponent('blog_preview_card.php', blogPost: $posts->get(1)); ?>
  <?= $page->renderComponent('blog_preview_card.php', blogPost: $posts->get(2)); ?>
</section>

<section class="past-posts">
  
  <?php foreach ($posts->slice(3, 6) as $post): ?>
    <?= $page->renderComponent('blog-preview_card.php', blogPost: $post); ?>    
  <?php endforeach ?>
  
</section>

<?= $page->renderPartial('site_footer.php'); ?>

So first off, we've really started to use our renderComponents method and component files. We also implemented a renderPartial as speculated upon above. Each does a similar thing, but having separate methods makes everything clear, handles paths, but still has a similar interface when calling them.

A big thing to notice here is that at no point have we added any markup to our page classes, and no business logic to our templates. If we need to find anything, we know where to look just by glancing at the template. Ultimate maintainability.

Here's our blog_preview_card.php component:

<?php namespace ProcessWire; ?>

<!-- /site/templates/components/blog_preview_card.php -->

<article class="blog-preview-card card">
  <img src="<?= $blogPost->blog_image->url; ?>" alt="<?= $blogPost->blog_image->description; ?>">
  
  <h2><?= $blogPost->title; ?></h2>
  
  <div class="blog-summary">
  	<?= $blogPost->blog_summary; ?>
  </div>
  
  <span class="blog-read-time"><?= $blogPost->readTime(); ?></span>
  
  <a href="<?= $blogPost->url; ?>">Read More</a>
</article>

I am liking how well this is working out! Page classes have done a ton of heavy lifting here:

• We're using our renderComponent method to it's maximum potential and it's payed off in spades
• Our template couldn't be cleaner or more easily maintainable
• BlogPostPage.php has taken care of all of our needs as far as delivering the PageArray of posts and all our template does is output the data as needed
• Our "card" component will render the same thing everywhere and we can update how that looks globally with changes to one file

If you don't think this can get more awesome, or think this post is already too long, I have bad news for you and you should stop reading now.

Still here? Let's create a BlogPostPage class and add a method:

<?php namespace ProcessWire;

// /site/classes/BlogPostPage.php

class BlogPostPage extends BasePage {

  // ... Other page methods, like readTime()
 
  public function relatedPosts(int $limit = 3): PageArray {
    return wire('pages')->get('template=blog')->latestPosts(
      limit: $limit,
      includePinnedPost: false,
      categoryId: $this->blog_category?->id
    );
  }
}

The BlogPage::latestPosts method is really flexing it's muscle here. We've used it in two different places for different purposes but requesting similar data, blog posts. If you noticed, we're also specifying a category for this blog since we have a page select field that references a blog category. That was a parameter that we included back in our BlogPage::latestPosts() method.

So, blog posts have a "You might also be interested in..." section with posts in the same category as the that one that a visitor has just read. With page classes this couldn't be easier to add, so let's use the relatedPosts method we just created in BlogPostPage.php in our blog-post.php template:

<?php namespace ProcessWire;

// /site/templates/blog-post.php

echo $page->renderPartial(
  'site_header.php',
  bodyClasses: 'blog-post',
  metaDescription: $sanitizer->truncate($page->blog_summary, 160)
);
?>

<!-- The page hero, blog content, stuff, etc. -->

<section class="related-posts">
  
  <?php foreach ($page->relatedPosts() as $post): ?>
    <?= $page->renderComponent('blog_preview_card.php', blogPost: $post); ?>
  <?php endforeach ?>
  
</section>

<?= $page->renderPartial('site_footer.php'); ?>

We've just added a related posts feature in *checks stopwatch* seconds. This project is going so fast that you can already hear the crack of the cold beer after a job well done.

One more example, and I'll let you decide if this is too much, or feels just right. We want a blog feed on our home page. So before we go to the home.php template, let's do what we do (surprise, it's a page class):

<?php namespace ProcessWire;

// /site/classes/HomePage.php

class HomePage extends BasePage {

  // Other HomPage methods...
 
  public function blogFeed(int $limit = 3): PageArray {
    return wire('pages')->get('template=blog')->latestPosts(limit: $limit);
  }
 
}

At first glance, this might seem like a bit much. Why create a method in our page class that is so short and simple? We could just call $pages->get('template=blog')->latestPosts(3) inside our template and get away with it just fine. Here's why I think it's worth creating a dedicated page class method:

• This creates yet another example of predictability between templates
• It promotes thie philosophy I like of page classes talking to page classes
• It's likely that we'll have other more complex methods in the HomePage class, keeping them together feels right and helps with uniformity- we always know where to look when seeing custom methods
• If we need to make a change to the BlogPage::latestPosts() method that affect how other page classes call that method, we don't have to root around in our templates to make any changes.
• It's pretty nice to see that thus far we have only ever referenced the $page object in our templates! There aren't any calls to $pages because our template is really about doing one thing- rendering the current page without caring about other pages. That's not to say that we can't, or shouldn't, use other ProcessWire objects in our templates, but it's still impressive how much we've been able to scope the data that we're working with in each template.

I truly love the page classes feature in ProcessWire and even though this is a deeper dive than my other post, this really is still just scratching the surface because we can imagine having more complex behavior and other benefits. Here are some from my experience:

• Handling AJAX calls to the same page. Choosing how and what type of content is returned when the page is loaded is really nice. This can be done with hooks, but I really like page classes handling things like this in-context.
• Working with custom sessions between one or more pages. Creating a trait that shares session behavior between page classes is a great way to extend functionality while keeping it scoped.
• Adding external API calls and whatever complexity that may entail
• Provides the ability to add significant complexity to our templates in the admin yet little to no additional complexity in template files. The basic "pinned post" and form embed features are just the start
• As you can imagine, this makes replicating code you use often between projects trivial
• Page classes provide a home for logic that otherwise would be stuck in a template, or relegated to a messy functions.php file. No more functions.php ever.
• We met every single goal I listed here at the beginning
• Every single template thus far only uses if statements and loops
• BasePage could have a "bootApplication" method if needed that does things for every page and is called in ready.php. This is also a great way to create a "bootable" method in all of your page classes where bootApplication could call a bootPage method in your page classes if it exists.

Thanks for coming to my TED talk. Hope you find this useful! If you have any questions, corrections, use cases, or things to add, the comments below are open and I'd love to hear them!

[zilli]

Wow, this is so nice. Thank you very much!

Have you considered writing a beginner's course on PHP OOP using ProcessWire as the main tool? 😊

[FireWire]

7 hours ago, zilli said:

Wow, this is so nice. Thank you very much!

Very happy to hear you enjoyed it!.

7 hours ago, zilli said:

Have you considered writing a beginner's course on PHP OOP using ProcessWire as the main tool?

Writing a course on anything hasn't ever crossed my mind haha.

I just put this together to share a great ProcessWire feature that has really boosted my workflow and thought maybe sharing some examples might be useful to others. I hadn't thought about this post as a walkthrough on OOP specifically, but I did want to be descriptive in a way that would be useful to as many people as possible- whether you are familiar with OOP or not, and without any assumptions. All said, I'm happy to try and answer questions if it would help anyone 🙂

[Alpina]

This is great stuff! Thank you!

@FireWire, As a beginner, I would love to learn how you usually set up a simple institutional website. It would be nice to see how you do.

[gornycreative]

Yeah custom page classes are absolutely essential to everything I put together.

It's really nice to be able to populate interfaces for different page types this way - e.g. I have a jsonld method I attach to various page classes that allow me to segregate the structured data and custom tailor it for each class - but in various templates I can simple $page->jsonld() and not think about the schema more than once for each page class. I already know the right fields for a given page type will go in the right spots in the schema output.