PHP gets all child nodes under any parent node of the tree structure

One 、 explain

• Known data table has fields ：id, pid, name Etc , To any parent node pid, Need to find out ： All child nodes under the parent node
• If the data exists in the data table , Through here queryAll Method simulation sql Inquire about The way to achieve

Two 、 Code

    public function test()
    {
    
        $pid = isset($_REQUEST['pid']) ? $_REQUEST['pid'] : 1;

        $subIds = [];
        $self = new self();
        self::getSubIds($pid, $self, $subIds);

        var_export($subIds);
        die;
    }

    public function getSubIds($pid, self $dao, &$subIds)
    {
    
        $param = [];
        if (is_array($pid)) {
    
            $param['in'] = $pid; // The superior pid IN  Inquire about 
        } else {
    
            $param['eq'] = $pid; // The superior  pid =  Inquire about 
        }

        // According to the parent node , Find child nodes of lower level 
        $subList = $dao->searchAll($param);
        if (empty($subList)) {
    
            return $subIds;
        }

        $tempSubIds = array_column($subList, 'id');  // Get all the subordinates of this node id
        $subIds = array_merge($subIds, $tempSubIds); // User subordinate ID Merge 

        $this->getSubIds($tempSubIds, $dao, $subIds);
    }

    // Simulate all operations of data table query 
    public function searchAll($param)
    {
    
        $result = [];
        $data = self::getData();

        if (array_key_exists('eq', $param)) {
     // Equal to operation 
            $searchValue = $param['eq'];
            foreach ($data as $value) {
    
                if ($searchValue == $value['pid']) {
    
                    $result[] = $value;
                }
            }
        }
        if (array_key_exists('in', $param)) {
     //in Inquire about 
            $searchArray = $param['in'];
            foreach ($data as $value) {
    
                if (in_array($value['pid'], $searchArray)) {
    
                    $result[] = $value;
                }
            }
        }

        return $result;
    }

    // Simulate the data stored in the data table 
    public function getData()
    {
    
        return [
            ['id' => 1, 'pid' => 0, 'name' => ' mobile phone '],
            ['id' => 2, 'pid' => 1, 'name' => 'A mobile phone '],
            ['id' => 3, 'pid' => 2, 'name' => 'A Mobile phone charger '],
            ['id' => 4, 'pid' => 2, 'name' => 'A Mobile phone earphone '],
            ['id' => 5, 'pid' => 1, 'name' => 'B mobile phone '],
            ['id' => 6, 'pid' => 5, 'name' => 'B Mobile phone charger '],
            ['id' => 7, 'pid' => 5, 'name' => 'B Mobile phone earphone '],
            ['id' => 8, 'pid' => 7, 'name' => 'B Mobile phone headset left headset '],
            ['id' => 9, 'pid' => 7, 'name' => 'B Mobile phone headset right headset '],
            ['id' => 10, 'pid' => 0, 'name' => ' The computer ']
        ];
    }