How to Create Multi level category hierarchy ( Category Tree ) - codeigniter

Question

I want to simply create a multilevel category hierarchy from mysql

Category table:

________________________________________________________________________
| id              |  parent_id     | name
————————————————————————————————————————————————————————————————————————
| 1               |  0             | Root
| 2               |  1             | Sub category of root
| 3               |  0             | category 1
| 4               |  3             | sub category of category 1
| 5               |  4             | sub category of first sub category of category 1
————————————————————————————————————————————————————————————————————————

php

public function getCategoryTree($level = 0) {
    $rows = $this->db
            ->select(‘id,parent_id,name’)
            ->where(‘parent_id’, $level)
            ->get(‘categories’)
            ->result();

    if (count($rows) > 0) {
        foreach ($rows as $row) {
            $rows = $this->getCategoryTree($row->id);
        }
    }
  //return $rows;
}


echo $rows;

// output will be show as string so i have to return this string in a variable

Root
—Sub category of root
category 1
—sub category of category 1
——sub category of first sub category of category 1

Answer 1

The biggest problem in your code was that you were overwriting $rows inside your foreach loop.

Additionally, with a recursive solution, like you've gone for, it's important to keep track of what's been returned from the inner calls to the function/method.

Also, I've added an order by, to make sure the root category appears first.

protected function getCategoryTree($level = 0, $prefix = '') {
    $rows = $this->db
        ->select('id,parent_id,name')
        ->where('parent_id', $level)
        ->order_by('id','asc')
        ->get('categories')
        ->result();

    $category = '';
    if (count($rows) > 0) {
        foreach ($rows as $row) {
            $category .= $prefix . $row->name . "\n";
            // Append subcategories
            $category .= $this->getCategoryTree($row->id, $prefix . '-');
        }
    }
    return $category;
}

public function printCategoryTree() {
    echo $this->getCategoryTree();
}