Question

Problem:

I am trying to build a recursive tree using a function and data from a MySQL. However, the results are not as expected.

PHP code:

function buildTree($root, $next = array()) 
{
    // Sanitize input
    $root = (int) $root;

    // Do query
    $query = "SELECT CID, Item, Parent FROM betyg_category WHERE Status = '1' AND Parent = '{$root}'";
    $result = mysql_query($query) or die ('Database Error (' . mysql_errno() . ') ' . mysql_error());

    // Loop results
    while ($row = mysql_fetch_assoc($result)) 
    {
      $next[$row['CID']] = array (
                                'CID' => $row['CID'], 
                                'Item' => $row['Item'], 
                                'Parent' => $row['Parent'], 
                                'Children' => buildTree($row['CID'], $next)
                            );
    }

    // Free mysql result resource
    mysql_free_result($result);

    // Return new array
    return $next;
}

$testTree = buildTree(0);

echo "<xmp>".print_r($testTree, true)."</xmp>";

The table in the database look like this:

I would like the array to be like this:

Array
(
    [1] => Array
    (
        [CID] => 1
        [Item] => Litteratur
        [Parent] => 0
        [Children] => Array
            (
                [2] => Integration av källorna
                [3] => Belysning av egna resultat
                [4] => Referenser
            )

    )

    and so forth..
)

That is to say, for each parent => produce children, then move on to next parent, etc. Thank you in advance for any advice.

Answer 1

You do not need recursion here. In fact, it will be very inefficent since you end up with a SELECT N+1 issue. Just order the result set by parent:

$query = "SELECT CID, Item, Parent FROM betyg_category WHERE Status = '1' ORDER BY Parent";
$result = mysql_query($query);

$tree = array();
while($row = mysql_fetch_assoc($result)) {
    if($row['Parent'] == 0) {
        $row['Children'] = array();
        $tree[$row['CID']] = $row;
    } else {
        $tree[$row['Parent']]['Children'][] = $row;
    }
}

This will produce the following:

Array
(
    [1] => Array
        (
            [CID] => 1
            [Item] => Litteratur
            [Parent] => 0
            [Children] => Array
                (
                    [0] => Array
                        (
                            [CID] => 2
                            [Item] => Integration av källorna
                            [Parent] => 1
                        )

                    [1] => Array
                        (
                            [CID] => 3
                            [Item] => Belysning
                            [Parent] => 1
                        )

                    [2] => Array
                        (
                            [CID] => 4
                            [Item] => Referenser
                            [Parent] => 1
                        )

                )

        )

    [5] => Array
        (
            [CID] => 5
            [Item] => Validitet
            [Parent] => 0
            [Children] => Array
                (
                    [0] => Array
                        (
                            [CID] => 6
                            [Item] => Huvudsyfte
                            [Parent] => 5
                        )

                )

        )

)

If you only want the name of each children, change, use $tree[$row['Parent']]['Children'][] = $row['Item']; instead.