cakePHP 3多次保存 - 如何将其与Form Helper一起使用

http://book.cakephp.org/3.0/en/orm/saving-data.html#converting-multiple-records

I am reading this, so i want my data just like the cookbook

//Details Controller

  $data = [
                'product_id' => '1'
                [
                    'size' => 'm',
                    'inventory' => 1
                ],
                [
                    'size' => 'l',
                    'inventory' => 1
                ],

            ];

//add_multiple.ctp I just assumed it was like this

    <?= $this->Form->create() ?>
    <?php 
        echo $this->Form->input('product_id');
        echo $this->Form->input('size');
        echo $this->Form->input('inventory');
        echo $this->Form->input('size');
        echo $this->Form->input('inventory');
        echo $this->Form->input('size');
        echo $this->Form->input('inventory');
  ?>
  <?= $this->Form->button(__('Submit')) ?>
  <?= $this->Form->end() ?>

i am using the product_id as a FK This returns me debug($this->request->data)

[
    'style_name' => 'blank',
    'product_id' => '1',
    'size' => 'L',
    'inventory' => '12'
]

All that effort to write my question, anyway i figured it out, it was rather simple

    echo $this->Form->input('1.size');
    echo $this->Form->input('1.inventory');
    echo $this->Form->input('2.size');
    echo $this->Form->input('2.inventory');
    echo $this->Form->input('3.size');
    echo $this->Form->input('3.inventory');