implementing multi-level "iterator" in PHP

Question

I'm trying to create a iterator like this one, for a list of comments:

// the iterator class, pretty much the same as the one from the php docs...
abstract class MyIterator implements Iterator{

  public $position = 0,
         $list;

  public function __construct($list) {
    $this->list = $list;
    $this->position = 0;
  }

  public function rewind() {
    $this->position = 0;
  }

  public function current() {
    return $this->list[$this->position];
  }

  public function key() {
    return $this->position;
  }

  public function next() {
    ++$this->position;
  }

  public function valid() {
    return isset($this->list[$this->position]);
  }
}

The comment iterator:

class MyCommentIterator extends MyIterator{

  public function current(){
    return new Comment($this->list[$this->position]);
  }    
}

And this is how I use it:

$comments = GetComments(); // gets the comments from the db
if($comments): ?>

  <ol>
    <?php foreach(new MyCommentIterator($comments) as $comment): ?>
    <li>
      <p class="author"><?php echo $comment->author(); ?></p>

      <div class="content">
        <?php echo $comment->content(); ?>
      </div>

      <!-- check for child comments and display them -->

    </li>
    <?php endforeach; ?>
  </ol>

<?php endif; ?>

So everything is working fine, besides one thing: I can't figure it out how to process nested comments :(

The $comments array returns a flat list of comments, like:

[0] => object(
    'id' => 346,
    'parent' => 0,  // top level comment
    'author' => 'John',
    'content' => 'bla bla'         
  ),

[1] => object(
    'id' => 478,
    'parent' => 346,  // child comment of the comment with id =346
    'author' => 'John',
    'content' => 'bla bla'         
  )
...

I need to somehow be able to check for child comments (on multiple levels) and insert them before the </li>'s of their parent comments...

Any ideas?

Answer 1

Recursion is your friend.

displaycomment(comment):
    $html .= "<ol>" . comment->html;
    foreach comment->child:
        $html .= "<li>" . displaycomment(child) . "</li>";
    $html .= "</ol>";
    return $html;

All code appearing in this post is pseudo. Any resemblance to real code, working or broken, is purely coincidental.

Answer 2

You might want to look into the RecursiveIterator Interface ^{PHP Manual}. If you extend your iterator with the methods by that interface, you're able to iterate over your comments with an instance of RecursiveIteratorIterator ^{PHP Manual} sequentially.

However as your output is a flat list, you need to take care of the logic for the levels on your own, e.g. inserting <ol> per depth up, and </ol> per depth down.

Use the flags to control the order how children are traversed.

Answer 3

You are using a flat array, but in reality, the items of that array are a tree or hierarchical data structure.

You are basically displaying a sequential list. Maybe you should construct a tree / hierarchical data structure first, without displaying, and later display data from the tree list.

/* array */ function FlatArrayToTreeArray(/* array */ $MyFlatArray)
{
  ...
}

/* void */ function IterateTree(/* array */ $MyTreeArray)
{
  ...
}

/* void */ function Example() {
  $MyFlatArray = Array(
  0 => object(
      'id' => 346,
      'parent' => 0,  // top level comment
      'author' => 'John',
      'title' => 'Your restaurant food its too spicy',
      'content' => 'bla bla'         
    ),
  1 => object(
      'id' => 478,
      'parent' => 346,  // child comment of the comment with id =346
      'author' => 'Mike',
      'title' => 'Re: Your restaurant food its too spicy',
      'content' => 'bla bla'         
    ),  
  2 => object(
      'id' => 479,
      'parent' => 478,  // child comment of the comment with id =346
      'author' => 'John',
      'title' => 'Re: Your restaurant food its too spicy',
      'content' => 'bla bla'         
    ),  
  3 => object(
      'id' => 479,
      'parent' => 346,  // child comment of the comment with id =346
      'author' => 'Jane',
      'title' => 'Re: Your restaurant food its too spicy',
      'content' => 'bla bla'         
    )
  );

  $MyTreeArray = FlatArrayToTreeArray($myflatarray);

  IterateTree($MyTreeArray);
} // function Example()

Cheers.