Dynamic Pages

Dynamic Pages

So far we only have a static page with not much functionality. Just having a hello world example is not very useful, so let’s go beyond that and add some real functionality to our application.

Our first feature will be dynamic pages generated from markdown files.

Create a Page controller with the following content:

<?php declare(strict_types = 1);

namespace Example\Controllers;

class Page
{
    public function show($params)
    {
        var_dump($params);
    }
}

Once you have done that, add a new route:

['GET', '/{slug}', ['Example\Controllers\Page', 'show']],

Now try and visit a few urls, for example http://localhost:8000/test and http://localhost:8000/hello. As you can see, the Page controller is called every time and the $params array receives the slug of the page.

So let’s create a few pages to get started. We won’t use a database yet, so create a new folder pages in the root folder of your project. In there add a few files with the file extensions .md and add some text to them. For example page-one.md with the content:

This is a page.

Now we will have to write some code to read the proper file and display the content. It might seem tempting to just put all that code into the Page controller. But remember Separation of Concerns. There is a good chance that we will need to read the pages in other places in the application as well (for example in an admin area).

So let’s put that functionality into a separate class. There is a good chance that we might switch from files to a database later, so let’s use an interface again to make our page reader decoupled from the actual implementation.

In your ‘src’ folder, create a new folder Page. In there we will put all the page related classes. Add a new file in there called PageReader.php with this content:

<?php declare(strict_types = 1);

namespace Example\Page;

interface PageReader
{
    public function readBySlug(string $slug) : string;
}

For the implementation, create a FilePageReader.php file. The file will looks like this:

<?php declare(strict_types = 1);

namespace Example\Page;

use InvalidArgumentException;

class FilePageReader implements PageReader
{
    private $pageFolder;

    public function __construct(string $pageFolder)
    {
        $this->pageFolder = $pageFolder;
    }

    public function readBySlug(string $slug) : string
    {
        return 'I am a placeholder';
    }
}

As you can see we are requiring the page folder path as a constructor argument. This makes the class flexible and if we decide to move files or write unit tests for the class, we can easily change the location with the constructor argument.

You could also put the page related things into it’s own package and reuse it in different applications. Because we are not tightly coupling things, things are very flexible.

This will do for now. Let’s create a template file for our pages with the name Page.html in the templates folder. For now just add {{ content }} in there.

Add the following to your Dependencies.php file so that the application know which implementation to inject for our new interface. We also define the the pageFolder there.

$injector->define('Example\Page\FilePageReader', [
    ':pageFolder' => __DIR__ . '/../pages',
]);

$injector->alias('Example\Page\PageReader', 'Example\Page\FilePageReader');
$injector->share('Example\Page\FilePageReader');

Now go back to the Page controller and change the show method to the following:

public function show($params)
{
    $slug = $params['slug'];
    $data['content'] = $this->pageReader->readBySlug($slug);
    $html = $this->renderer->render('Page', $data);
    $this->response->setContent($html);
}

To make this work, we will need to inject a Response, Renderer and a PageReader. I will leave this to you as an exercise. Remember to use all the proper namespaces. Use the Homepage controller as a reference.

Did you get everything to work?

If not, this is how the beginning of your controller should look now:

<?php declare(strict_types = 1);

namespace Example\Controllers;

use Http\Response;
use Example\Template\Renderer;
use Example\Page\PageReader;

class Page
{
    private $response;
    private $renderer;
    private $pageReader;

    public function __construct(
        Response $response,
        Renderer $renderer,
        PageReader $pageReader
    ) {
        $this->response = $response;
        $this->renderer = $renderer;
        $this->pageReader = $pageReader;
    }
...

So far so good, now let’s make our FilePageReader actually do some work.

We need to be able to communicate that a page was not found. For this we can create a custom exception that we can catch later. In your src/Page folder, create a InvalidPageException.php file with this content:

<?php declare(strict_types = 1);

namespace Example\Page;

use Exception;

class InvalidPageException extends Exception
{
    public function __construct($slug, $code = 0, Exception $previous = null)
    {
        $message = "No page with the slug `$slug` was found";
        parent::__construct($message, $code, $previous);
    }
}

Then in the FilePageReader file add this code at the end of your readBySlug method:

$path = "$this->pageFolder/$slug.md";

if (!file_exists($path)) {
    throw new InvalidPageException($slug);
}

return file_get_contents($path);

Now if you navigate to a page that does not exist, you should see an InvalidPageException. If a file exists, you should see the content.

Of course showing the user an exception for an invalid URL does not make sense. So let’s catch the exception and show a 404 error instead.

Go to your Page controller and refactor the show method so that it looks like this:

public function show($params)
{
    $slug = $params['slug'];

    try {
        $data['content'] = $this->pageReader->readBySlug($slug);
    } catch (InvalidPageException $e) {
        $this->response->setStatusCode(404);
        return $this->response->setContent('404 - Page not found');
    }
    
    $html = $this->renderer->render('Page', $data);
    $this->response->setContent($html);
}

Make sure that you use an use statement for the InvalidPageException at the top of the file.

Try a few different URLs to check that everything is working as it should. If something is wrong, go back and debug it until it works.

And as always, don’t forget to commit your changes.


License