PHP - 如何构建树结构列表？

PHP - How to build tree structure list?

提问by Vaiman Hunor

So, my problem is, that I want to build a tree of these 2 tables:

所以，我的问题是，我想构建这两个表的树：

Parent table:
+-------+---------------+
| pr_id |  parent_name  |
+-------+---------------+
|   1   |       p       |
|   2   |      p_0      | 
|   3   |     p_0_1     | 
|   4   |       q       | 
+-------+---------------+

Child table:
+-------+---------------+---------------------------+
| ch_id |     pr_id     |        child_name         |
+-------+---------------+---------------------------+
|   1   |       1       |            p_0            |
|   2   |       1       |            p_1            |
|   3   |       2       |           p_0_0           |
|   4   |       2       |           p_0_1           |
|   5   |       3       |          p_0_1_0          |
|   6   |       3       |          p_0_1_1          |
|   7   |       4       |            q_0            |
|   8   |       4       |            q_1            |
+-------+---------------+---------------------------+

And the Tree should look like:

树应该看起来像：

• p
  • p_0
    • p_0_0
    • p_0_1
      • p_0_1_0
      • p_0_1_1
• q

• 磷
  • p_0
    • p_0_0
    • p_0_1
      • p_0_1_0
      • p_0_1_1
• q

Can anybody help me out with a recursive solution??

有人可以帮我解决递归解决方案吗？

回答by Veerendra

You do not need to create 2 tables in the database for this you can maintain it like below from one table only

您不需要在数据库中创建 2 个表，您可以仅从一个表中维护它，如下所示

+-------+---------------+---------------------------+
|   id  |   parent_id   |           title           |
+-------+---------------+---------------------------+
|   1   |       0       |   Parent Page             |
|   2   |       1       |   Sub Page                |
|   3   |       2       |   Sub Sub Page            |
|   4   |       0       |   Another Parent Page     |
+-------+---------------+---------------------------+

The array generated will be like

生成的数组将类似于

Array
(
    [0] => Array
        (
            [id] => 1
            [parent_id] => 0
            [title] => Parent Page
            [children] => Array
                        (
                            [0] => Array
                                (
                                    [id] => 2
                                    [parent_id] => 1
                                    [title] => Sub Page
                                    [children] => Array
                                                (
                                                    [0] => Array
                                                        (
                                                            [id] => 3
                                                            [parent_id] => 1
                                                            [title] => Sub Sub Page
                                                        )
                                                )
                                )
                        )
        )
    [1] => Array
        (
            [id] => 4
            [parent_id] => 0
            [title] => Another Parent Page
        )
)

You need to use the below recursive function to achieve it

您需要使用以下递归函数来实现它

function buildTree(array $elements, $parentId = 0) {
    $branch = array();

    foreach ($elements as $element) {
        if ($element['parent_id'] == $parentId) {
            $children = buildTree($elements, $element['id']);
            if ($children) {
                $element['children'] = $children;
            }
            $branch[] = $element;
        }
    }

    return $branch;
}

$tree = buildTree($rows);

The algorithm is pretty simple:

算法非常简单：

1. Take the array of all elements and the id of the current parent (initially 0/nothing/null/whatever).
2. Loop through all elements.
3. If the parent_id of an element matches the current parent id you got in 1., the element is a child of the parent. Put it in your list of current children (here: $branch).
4. Call the function recursively with the id of the element you have just identified in 3., i.e. find all children of that element, and add them as children element.
5. Return your list of found children.

1. 获取所有元素的数组和当前父级的 id（最初为 0/nothing/null/whatever）。
2. 循环遍历所有元素。
3. 如果元素的 parent_id 与您在 1. 中获得的当前父 ID 匹配，则该元素是父元素的子元素。把它放在你当前孩子的列表中（这里：$branch）。
4. 使用您刚刚在 3. 中标识的元素的 id 递归调用该函数，即找到该元素的所有子元素，并将它们添加为子元素。
5. 返回您找到的孩子的名单。