Johannes Schlüter

PHP 5.3 is released and after the release stress is over my mind is open for new ideas. While relaxing yesterday I thought about many things, among them was the Resultset iterator I recently discussed.

Now I wondered where to go next with this and had the idea that an individual Resultset is a child of the whole result and this might be wrapped in an Recursive Iterator. For doing so we don't implement the Iterator interface but RecursiveIterator. RecursiveIterator extends a typical Iterator with two methods: hasChildren() and getChildren(). But now we have a problem: The Iterator returned by getChildren() has to be a RecursiveIterator, too, which makes sense, in general. But I want to return a MySQLi Resultset which isn't recursive - so making this a RecursiveIterator is wrong. My solution now is to introduce yet another Iterator which goes by the name of MySQLi_PseudoRecursiveResultIterator and is implemented by extending IteratorIterator which will wrap the MySQLi_Result and implements RecursiveIterator telling the caller that there are no children.

As a sidenote: In our experimental tree Andrey made MySQLi_Result an iterator but that's not yet in php.net's CVS (might need some more testing, and probably we might change the design there...) so I'm emulating this with MySQLi_Result::fetch_all() combined with an ArrayIterator, using the experimental code the constructor can be dropped.

So let's finally look at the code of these two classes:

<?php
class MySQLi_ResultsetIterator implements RecursiveIterator
{
    private $mysqli;
    private $counter = 0;
    private $current = null;
    private $rewinded = false;

    public function __construct(mysqli $mysqli) {
        $this->mysqli = $mysqli;
    }
    private function freeCurrent() {
        if ($this->current) {
            $this->current->free();
            $this->current = null;
        }
    }
    public function rewind() {
        if ($this->rewinded) {
            throw new Exception("Already rewinded");
        }
        $this->freeCurrent();
        $this->counter = 0;
        $this->rewinded = true;
    }
    public function valid() {
        $this->current = $this->mysqli->store_result();
        return (bool)$this->current;
    }
    public function next() {
        $this->freeCurrent();
        $this->counter++;
        $this->mysqli->next_result();
    }
    public function key() {
        return $this->counter;
    }
    public function current() {
        if (!$this->current) {
            throw new Exception("valid() not called");
        }
        return $this->current;
    }

    public function hasChildren() {
        return true;
    }
    public function getChildren() {
        return new MySQLi_PseudoRecursiveResultIterator($this->current);
    }
}

class MySQLi_PseudoRecursiveResultIterator
     extends IteratorIterator
     implements RecursiveIterator
{
    public function __construct(MySQLi_Result $result) {
        // This ctor can be dropped with the experimental bzr sources
        // as IteratorIterator::__construct() directly works with
        // MySQLi_Result
        parent::__construct(new ArrayIterator($result->fetch_all()));
    }
    public function hasChildren() {
        return false;
    }
    public function getChildren() {
        throw new Exception("This should never be called");
    }    
}
?>

Now we can use this code. For properly using a RecursiveIterator one should use a RecursiveIteratorIterator (RII). To get some nice labels I'm extending the RII and then have a single foreach:

<?php
class MyRecursive_IteratorIterator
     extends RecursiveIteratorIterator
{
    public function __construct(MySQLi $mysqli, $flags = 0) {
        parent::__construct(
                new Mysqli_ResultSetIterator($mysqli),
                $flags | RecursiveIteratorIterator::LEAVES_ONLY);
    }

    public function beginChildren() {
        echo "Next ResultSet:\n";
    }
}

$mysqli = new MySQLi("localhost", "root", "", "test");

$query  = "SELECT 1,2 UNION SELECT 3, 4;".
          "SELECT 'hi world' UNION SELECT 'foobar'";
if ($mysqli->multi_query($query)) {
    foreach (new MyRecursive_IteratorIterator($mysqli) as $key => $row) {
        printf("    %s\n", $row[0]);
    }
}
?>

Now calling this code gives us a result similar to the following:

Next ResultSet:
    1
    3
Next ResultSet:
    hi world
    foobar

Isn't that nice? - I think that's a cool API! What do you think? Do you have use cases for such an API? Should we implement this in C and bundle it with PHP? Any feedback welcome!