PHP/MVC : in this case, how to use DTO?

Question

I'm new to OOP and MVC with PHP, and I'm currently learning by making my own custom framework from scratch, for testing purposes. I have set up my controllers, models and views and everything works fine.

My app has the following architecture :

It’s a small blog that follows the rules of the MVC pattern. To summarize, it works like this :

• The called Controller will fetch the data using the right models
• Models return objects of the class \Classes\{MyObject}
• Controller call the right template to render the view, and passes it the data and objects to display

The problem

In some views, I need to display related data. For example, in the article view, I need to display the author's first name. In the database, an article contains only the author’s ID, not his first name : this is the same thing in my class \Classes\Article.

What I've tried

To display the author’s first name in my view, I've updated the model Find method to use a LEFT JOIN in the SQL query. Then, I've updated my \Classes\Article class to have a user_firstname property :

class Article
{
    private $pk_id;
    private $title;
    private $excerpt;
    private $content;
    private $created_at;
    private $fk_user_id;
    private $updated_at;
    private $user_firstname; // <-- I've added this property to retrieve author's firstname

// (...)
}

What I did works well, but my teacher tells me it’s not the right way to do it because the author’s firstname is not part of the definition of an article.

In this case, my teacher tells me to use a DTO (Data Transfert Object) between Article and User classes.

Questions

• What is the right way to set up a DTO in this case?
• Do I need to create a new ArticleUserDTO class in a new namespace ?
• How to use it ?

I think I understood the problem : the Article class should only contain what defines an article. But I can’t understand the logic of setting up a DTO. I’ve done some research on it, I understand the usefulness of the DTO but I can’t set up into my app.

Answer 1

Setting up a DTO in my app was easy ! As mentioned by @daremachine, the diagram below helped me to understand what a DTO is for.

Diagram source : martinfowler.com

We can see DTOs as an object assembler, in which we place all the elements we need on the view side.

For example, in the post view of an article, I needed to display other items, such as the author and posted comments. So I have created a Post class that groups all these items.

Setting up a DTO

In my \Classes\ namespace, I've created a new Post class. First, we define the properties we will need. Then we add the getters and setters for each of them. Finally, we set up the constructor, which will call each of the classes we need in the view.

namespace Classes;

use DateTime;

class Post
{
    private int $pk_id;
    private string $title;
    private string $excerpt;
    private string $content;
    private DateTime $created_at;
    private DateTime $updated_at;
    private int $author_id;
    private string $author_firstname;
    private array $comments;

    public function __construct(Article $article, User $author, array $comments)
    {
        $this->setPkId($article->getId());
        $this->setTitle($article->getTitle());
        $this->setExcerpt($article->getExcerpt());
        $this->setContent($article->getContent());
        $this->setCreatedAt($article->getCreatedAt());
        $this->setUpdatedAt($article->getUpdatedAt());
        $this->setAuthorId($article->getAuthorId());
        $this->setAuthorFirstname($author->getFirstname());
        $this->setComments($comments);
    }

    /**
     * @param int $pk_id
     */
    public function setPkId(int $pk_id): void
    {
        $this->pk_id = $pk_id;
    }

    /**
     * @return int
     */
    public function getPkId(): int
    {
        return $this->pk_id;
    }

    // (etc)
}

We now need to update the ArticleController, which should no longer pass the Article, Comment and User objects, but only the new Post object.

namespace Controllers;

class ArticleController extends Controller
{
  // (...)

     /**
     * Get an article and display it
     *
     * @return void
     */
    public function show(): void
    {
        // (...)

        // Find Article :
        $article = $this->articleModel->find($article_id);

        if (!$article) {
            Http::error404();
        }

        // Find Comments :
        $commentaires = $this->commentModel->findAllByArticle($article_id);

        // Find User (author)
        $user = $this->userModel->find($article->getAuthorId());

        // Data Transfert Object instance :
        $post = new Post($article, $user, $commentaires);

        $pageTitle = $post->getTitle();
        // Pass DTO to view :
        Renderer::render('articles/show', compact('pageTitle', 'post'));
    }
}

We just need to update our view to use the new Post object and it's done ! Thanks to @daremachine for his help :)