I have written my own shipping method and hooked into WooCommerce. I've used the shipping class from the WooCommerce docs, works like a charm for most of it. This is my constructor:

/**
 * Constructor. The instance ID is passed to this.
 */
public function __construct( $instance_id = 0 ) 
{
    $this->id                 = 'my_shipping_id';
    $this->instance_id        = absint($instance_id);
    $this->method_title       = __('My shipping title');
    $this->method_description = __('shipping description');
    $this->supports = array(
        'shipping-zones',
        'instance-settings',
    );
    $this->instance_form_fields = array(
        'enabled' => array(
            'title'   => __('Enable'),
            'type'    => 'checkbox',
            'label'   => __('Enable this shipping method'),
            'default' => 'yes',
        ),
    );
    $this->enabled = $this->get_option('enabled');
    $this->title   = 'My shipping title';

    add_action('woocommerce_update_options_shipping_' . $this->id, array( $this, 'process_admin_options'));
}

Then I have the calculate_shipping method. This method calls our API for possible shipping options and rates and these are added to Woo through $this->add_rate()

            $rate = array(
            'id' => 'my_shipping_method_' . $option->method,
            'label' => $methodNames[$option->method],
            'cost' => $option->price,
        );

        // Register the rate
        $this->add_rate($rate);

So far this works like a charm. The checkout shows all options and I can place orders and the backend shows the right shipping title. This is where it goes wrong. The order is stored with the shipping ID from the constructor class, but with the title from the $this->add_rate() function. Therefore all shipping methods coming from the API look the same in the DB.

I would like to process this later automatically by selecting the shipment ID so we know which method to use.

Did I take the wrong turn somewhere and is this not possible? Or am I missing something?

I've made a custom shipping class for WooCommerce. In the calculate_shipping function an API request is done to our server requesting the possible shipping methods. This can result in one or multiple rates.

I have integrated this as follows in the calculate_shipping() function

    // Make a shipping rate for each result
    foreach ($quote->shipping_options as $option) {

        $rate = array(
            'id' => 'my_method_'.$option->id,
            'label' => $methodNames[$option->name],
            'cost' => $option->price,
        );

        // Register the rate
        $this->add_rate($rate);
    }

This displays the right options, uses the right rate and in the WooCommerce admin I can see which method was used. So far, so good.

The issue is:

The order is stored with the shipping ID from the custom shipping class and the label of the chosen rate.

How do I recognize programmatically which shipping method was used? I don't want to match on label for obvious reasons, and the ID is wrong. Can I store an identifier or change this behaviour?