Magento 2: How does the category tree/node work?

Question

I must admit that I am having trouble understanding the category tree/node thing in magento. I have extended the Topmenu class to build my own supermenu. It works fine except the category children are always sorted by their id instead of the defined sort order.

So I tried to dig into this but I simply cannot wrap my head around how magento actually pulls and organizes the categories from the database. It all boils down to this function:

public function getMenu()
{
    if (!$this->_menu) {
        $this->_menu = $this->nodeFactory->create(
            [
                'data' => [],
                'idField' => 'root',
                'tree' => $this->treeFactory->create()
            ]
        );
    }
    return $this->_menu;
}

Somehow magento magically comes up with the categories here. Nowhere I see the typical collection which I could understand.

So my question is: can someone please explain to me how this tree/node thing works and how magento pulls the categories from the database? And in addition to that: how can I manipulate it to my needs? As mentioned I need to get the children sorted by sort order instead of their ids.

Answer 1

Have a look into the vendor/magento/module-catalog/Plugin/Block/Topmenu.php.

The method beforeGetHtml() adds the category data to the topmenu.