如何以递归方式构建具有未知树深度的<select>

Question

我有一个带有树数据结构的MySQL表.这些字段是_id,name和parentId.当记录没有父级时,parentId默认为0.这样我就可以构建一个数组,然后递归打印每条记录.

构建的数组如下所示:

Array
(
    [1] => Array
        (
            [parentId] => 0
            [name] => Countries
            [_id] => 1
            [children] => Array
                (
                    [2] => Array
                        (
                            [parentId] => 1
                            [name] => America
                            [_id] => 2
                            [children] => Array
                                (
                                    [3] => Array
                                        (
                                            [parentId] => 2
                                            [name] => Canada
                                            [_id] => 3
                                            [children] => Array
                                                (
                                                    [4] => Array
                                                        (
                                                            [parentId] => 3
                                                            [name] => Ottawa
                                                            [_id] => 4
                                                        )

                                                )

                                        )

                                )

                        )

                    [5] => Array
                        (
                            [parentId] => 1
                            [name] => Asia
                            [_id] => 5
                        )

                    [6] => Array
                        (
                            [parentId] => 1
                            [name] => Europe
                            [_id] => 6
                            [children] => Array
                                (
                                    [7] => Array
                                        (
                                            [parentId] => 6
                                            [name] => Italy
                                            [_id] => 7
                                        )

                                    [11] => Array
                                        (
                                            [parentId] => 6
                                            [name] => Germany
                                            [_id] => 11
                                        )

                                    [12] => Array
                                        (
                                            [parentId] => 6
                                            [name] => France
                                            [_id] => 12
                                        )

                                )

                        )

                    [8] => Array
                        (
                            [parentId] => 1
                            [name] => Oceania
                            [_id] => 8
                        )

                )

         )

 )

<ul>使用递归打印无序列表非常简单.这是我使用的功能:

function toUL ($arr) {

    $html = '<ul>' . PHP_EOL;

    foreach ( $arr as $v ) {

        $html.= '<li>' . $v['name'] . '</li>' . PHP_EOL;

        if ( array_key_exists('children', $v) ) {
            $html.= toUL($v['children']);
        }

    }

    $html.= '</ul>' . PHP_EOL;

    return $html;
}

但我坚持以<select>树形结构方式打印:

Countries
-- America
---- Canada
------ Ottawa
-- Asia
-- Europe
---- Italy
---- Germany
---- France
-- Oceania

我想打印的--次数与元素的深度一样多,但我不知道如何计算深度.

我的问题是:是否有可能在<select>不了解深度的情况下建立一个？

先感谢您.

Answer 1

传递一个参数来计算迭代次数 $pass

function toUL ($arr, $pass = 0) {

    $html = '<ul>' . PHP_EOL;

    foreach ( $arr as $v ) {           

        $html.= '<li>';
        $html .= str_repeat("--", $pass); // use the $pass value to create the --
        $html .= $v['name'] . '</li>' . PHP_EOL;

        if ( array_key_exists('children', $v) ) {
            $html.= toUL($v['children'], $pass+1);
        }

    }

    $html.= '</ul>' . PHP_EOL;

    return $html;
}