用 php 显示存储在数据库中的家谱树

Question

我的数据库 (mysql) 中有一个表，其下一个架构：

-----------------------------
- id  name         parent_id
-----------------------------
- 1   grandfather  NULL
- 2   father       1
- 3   uncle        1
- 4   son          2
- 5   brother      2
- 6   sister       2

我想通过以下方式在我的页面上显示它：

grandfather 
father
son
brother
sister
Uncle

（前序遍历）

这是我找到的最佳解决方案（不起作用）

$sql = "SELECT p1.id, p1.name, p1.parent_id FROM tree p1 ORDER BY p1.id";
$result = $conn->query($sql);

while($row = mysqli_fetch_assoc($result)) {
        arbol($row, $result);
};
function arbol($fila, $result) {
            echo $fila["name"] . "<br>";
            $flag = false;
            while($busqueda = mysqli_fetch_row($result)) {
                if($busqueda[2]==$fila["id"]){
                    $flag = true;
                    break;
                }
            };

            if ($flag){
                foreach ($result as $ruta) {
                    if($ruta["parent_id"]==$fila["id"]){
                        arbol($ruta, $result);
                    };
                };


            } else {
                return;
            }
        };
    };

因此，我第一次遍历到底部，但从未遍历树的其余部分：

Grandfather
parent
son

我做错了什么？或者你有什么建议？

注意：完成后我会有很多“祖父”，这就是为什么会有 while（我会在那里添加一个“parent_id=NULL”条件）。

编辑： 执行此操作后的行结构：

while( $row = mysqli_fetch_assoc( $result)){
    $resguard[] = $row;
}
print_r($resguard);

这是（为清楚起见而格式化）：

Array ( 
[0] => Array ( [id] => 1 [name] => Grandfather [parent_id] => ) 
[1] => Array ( [id] => 2 [name] => Parent [parent_id] => 1 ) 
[2] => Array ( [id] => 3 [name] => Uncle [parent_id] => 1 ) 
[3] => Array ( [id] => 4 [name] => Son [parent_id] => 2 ) 
[4] => Array ( [id] => 5 [name] => Brother [parent_id] => 2 ) 
[5] => Array ( [id] => 6 [name] => Sister [parent_id] => 2 ) 
)

Answer 1

这是一个适用于您的数据集并假设原始数据按 id 排序的示例（就像您的查询一样）。我相信要走的路是编写小（er）、简单（r）的函数，将数据转换成树并逐步遍历它。可能会像您一样从数组中进行遍历并一次性打印出来，但是我的大脑目前无法想到好的方法。

function make_tree($data) {
    $tree = [];

    foreach ($data as $node) {
        insert($tree, $node);
    }

    return $tree;
}

function insert(&$root, &$node) {
    if (!$root) {
        $root = $node;
    }
    else if ($root["id"] === $node["parent_id"]) {
        $root["children"][] = $node;
    }
    else if (array_key_exists("children", $root)) {
        foreach ($root["children"] as &$c) {
            if (insert($c, $node)) {
                break;
            }
        }
    }
}

function preorder(&$root) {
    if ($root) {
        yield $root;

        if (array_key_exists("children", $root)) {
            foreach ($root["children"] as $c) {
                yield from preorder($c);
            }
        }
    }
}

$data = [
    ["id" => 1, "name" => "Grandfather", "parent_id" => null],
    ["id" => 2, "name" => "Father", "parent_id" => 1],
    ["id" => 3, "name" => "Uncle", "parent_id" => 1],
    ["id" => 4, "name" => "Son", "parent_id" => 2],
    ["id" => 5, "name" => "Brother", "parent_id" => 2],
    ["id" => 6, "name" => "Sister", "parent_id" => 2]
];

$tree = make_tree($data);

foreach (preorder($tree) as $node) {
    echo $node["name"]."\n";
}

输出：

Grandfather
Father
Son
Brother
Sister
Uncle