Building Multi Level Menu Dynamically with PDO in PHP - php

Question

I have this data in my database:
id nameOfPerson parent
3 John NULL
4 Michel 3
5 Husam 4
6 Khalaf 5
7 Mark 5
----------------------------
and i want to display it in list like this
John
Michel
Husam
Khalaf
Mark
but in my code he just displayed
John
Michel
How i want to Displeyed all data according to parent like above list ?
this is my function whats the wrongs ?
public function familyTree(){
$query = "SELECT id, nameOfPerson, parent FROM person WHERE parent is null";
$statment = $this->db->prepare($query);
$statment->execute();
echo '<ul id ="family">';
while($family = $statment->fetch(PDO::FETCH_OBJ)){
echo '<li>'. $family->nameOfPerson;
$query1 = "SELECT id, nameOfPerson, parent FROM person WHERE parent = :id";
$statment1 = $this->db->prepare($query1);
$statment1->bindValue('id', $family->id);
$statment1->execute();
if($statment1->rowCount() > 0){
echo '<ul>';
while($family2 = $statment1->fetch(PDO::FETCH_OBJ)){
echo '<li>' . $family2->nameOfPerson . '</li>';
}
echo '</ul>';
}
echo '</li>';
}
echo '</ul>';
}

Answer 1

ASSUMPTIONS
Every child has only 1 parent.
CODE
First, I retrieve all data from DB table as it is not efficient to retrieve data individually for each parent increasing DB calls and affecting response time.
Build an associative array of parent and children where every parent has 2 details of each child - nameOfPerson and id.
Iterate over this array in a recursive way and keep building the list for each child and ultimately return them.
Refer SQL Fiddle for table rows.
<?php
$pdo = new PDO("mysql:dbname=newdummy;host=localhost","root","");
$query = $pdo->query("Select * from hierarchy");
$family_tree = [];
$root_parent = -1;
$root_parent_name = "";
function makeTree($query,&$family_tree,&$root_parent,&$root_parent_name){
while($row = $query->fetch(PDO::FETCH_ASSOC)){
if(is_null($row['parent'])){
$root_parent = $row['id'];
$root_parent_name = $row['nameOfPerson'];
}else{
if(!isset($family_tree[$row['parent']])){
$family_tree[$row['parent']] = [];
}
$family_tree[$row['parent']][] = array($row['nameOfPerson'],$row['id']);
}
}
}
function buildList($family_tree,$parent){
$list = "<ul>";
foreach($family_tree[$parent] as $each_child){
$list .= "<li>" . $each_child[0];
if(isset($family_tree[$each_child[1]])){
$list .= buildList($family_tree,$each_child[1]);
}
$list .= "</li>";
}
$list .= "</ul>";
return $list;
}
makeTree($query,$family_tree,$root_parent,$root_parent_name);
echo "<ul>";
echo "<li>$root_parent_name";
echo buildList($family_tree,$root_parent);
echo "</li>";
echo "</ul>";
OUTPUT
<ul>
<li>John
<ul>
<li>Michel
<ul>
<li>
Husam
<ul>
<li>khalaf</li>
<li>Mark</li>
</ul>
</li>
</ul>
</li>
<li>Tross</li>
<li>David</li>
</ul>
</li>
</ul>