如何使用 php 从子 ID 获取顶级父 ID？

Question

I am an amateur in PHP. I tried a lot of suggestions from here but I didn't get the result I need. I want to get the top parent id of a child. ex. For id=10 top parent is 8. This is the array I get from the database. Thanks in advance.

$events = mysqli_query($dbtmx,"SELECT * FROM tmetrix_events WHERE status='1'");
while($re=mysqli_fetch_assoc($events)){
  $array[] = array('id'=>$re['id'],'parent_id'=>$re['parent_id']);
}

And the array I am receiving is

Array
(
    [0] => Array
        (
            [id] => 5
            [parent_id] => 0
        )

    [1] => Array
        (
            [id] => 6
            [parent_id] => 5
        )

    [2] => Array
        (
            [id] => 7
            [parent_id] => 5
        )

    [3] => Array
        (
            [id] => 8
            [parent_id] => 0
        )

    [4] => Array
        (
            [id] => 9
            [parent_id] => 8
        )

    [5] => Array
        (
            [id] => 10
            [parent_id] => 9
        )

)

Now I want to find the top parent or root parent id of the child.

I tried Steverst1 and AymDev's code. But I am getting the result.

Answer 1

You can create a recursive function which will run through all parents until it finds 0 which I assume means there is no parent:

function get_top_parent(int $id, array $list): ?array
{
    // Find current item
    $key = array_search($id, array_column($list, 'id'));
    $item = $list[$key] ?? null;
    
    // Check if item has parent
    if (null !== $item && $item['parent_id'] !== 0) {
        // recursive call
        return get_top_parent($item['parent_id'], $list);
    }
    
    // No parent (or no item)
    return $item;
}

Tested on 3v4l.org : https://3v4l.org/PPm3K

Answer 2

Assumption that 0 in parent_id means that it is the parent we are looking for. So get the id of it.

$child_id = 10;
$parent = 0;
while ($child_id != 0) {
    foreach ($array as $key => $inner_arr) {
        $id = $inner_arr['id'];
        $parent_id = $inner_arr['parent_id'];
        if($id === $child_id){
            $child_id = $parent_id;
            $parent = $id;
        }
    }
}
echo $parent; // 8

Demo