Understanding application logic in MVC

Question

In my effort to understand MVC in a simple way (I'm trying to make a demo application of my own), I've followed Symfony2's Symfony2 versus Flat PHP material, I've changed some stuff along the way trying to "improve" the code adding some OOP practices, I made a DB class and changed their model from this:

<?php
// model.php
function open_database_connection()
{
    $link = mysql_connect('localhost', 'myuser', 'mypassword');
    mysql_select_db('blog_db', $link);

    return $link;
}

function close_database_connection($link)
{
    mysql_close($link);
}

function get_all_posts()
{
    $link = open_database_connection();

    $result = mysql_query('SELECT id, title FROM post', $link);
    $posts = array();
    while ($row = mysql_fetch_assoc($result)) {
        $posts[] = $row;
    }
    close_database_connection($link);

    return $posts;
}

to this (ignore the spanish please):

<?php
/**
 * @author Me
 * 
 */
/**
 * post.php: clase post, elemento de texto básico del blog
 */
class Post
{
    /**
     * titulo del post
     * @var string
     */
    private $title;

    /**
     * Constructor de la clase Post
     * @param string $title
     */
    function __construct($title)
    {
       $this->title = $title;
    }

    /**
     * Get para titulo del post.
     * @return string
     */
    public function getTitle()
    {
        return $this->title;
    }

    /**
     * Set para titulo del post.
     * @param  string $title
     * @return self
     */
    public function setTitle($title)
    {
        $this->title = $title;
        return $this;
    }

    public function getAllPosts()
    {
        //Ummm what?
    }
}

My problem is, where does this getAllPosts() method fit in my model post.php?, what am I doing wrong? the only thing that came to mind was creating the method as static but that would make no sense and I kNOW it should not be done like that...

Thanks in advance guys, seems like understanding this whole MVC, MVC-like structures in web development is giving me quite some trouble hehe...

NOTE: This has nothing to do with Symfony at all, I'm just trying to follow their simple MVC-like implementation (incluiding the way they create the Views (which apparently is not the "pure" way MVC should be implemented)).

Answer 1

You have to make two objects.

• Entity object - the one you made, representing the Post in database.
  • getTitle()
  • setTitle(title)
• Data access object - class managing the Post entities in database (createPost).
  • getAllPosts()
  • savePost(post)

Answer 2

You just need to remember that MVC is an architectural pattern which separates the Business Layer (Model), UI (View), Coordonator(Controller). Note that the Model is polymoprhic i.e it is more than just the database.

MVC is itself an implemntation of the Separation of Concerns (SoC) prinicple. What flat php does (or any language actually) is called Transaction Script and it's suitable only for simplistic (scripting) tasks.

When you want to have an application, a virtual product which provides many (complex) features, where requierements change over the time, you need a proper architecture that can help you modify things without breaking others.

In your code, the getAllPosts method is a violation of separation of concerns and also of the Single Responsability Principle (SRP) becasue the Post, besides modeling a Post has also the task to handle persistence.

MVC says to separate the Model and the View and to use the Controller to coordinate those two. This also means that the Controller should do only managing work i.e selecting the model and selecting the view (or another result). Don't put the data access into Controller unles it's a trivial, homework, prototype app. Keep you Controllers thin doing only what they need to do. If youre controller has more than 10 lines of code, it's a high probability that it's doing too much.

MVC is a very simple pattern, it's much harder to maintain the discipline to respect it.

Answer 3

You only implemented the "M" (the model) part of the MVC structure. Functionality concerning several entities is best left to the Controller that gets your brower's request. So you can go on to add a class like this (using the excellent Doctrine DBAL access layer):

class PostController {
  private $myDb;

  public function __construct(Doctrine\DBAL\Connection $db) {
    $this->myDb = $db;
  }

  public function get() {
    if (!isset($_REQUEST['id'])) {
      $allPosts = $this->myDb->fetchAll('SELECT * FROM Post');
    }
    // pass $allPosts to the view layer...
  }
}

Since the Doctrine guide explicitly warns about adding business logic to the controller: in my personal opinion simple code like fetching all records can go into the controller just fine. You can then wrap the data in model instances by using a Post constructor that accepts an array of column values. All the logic can then use your entity as recommended.

If your database access code gets more sophisticated and you find yourself constantly copying the same code snippets, you can start with StaNov's suggestion of building a separate data access layer. Until then, I really recommend

1. Stick with a library to do the low level database access
2. Use the most simple code possible that gets the job done. Complexity will haunt you soon enough.