Debugging Drupal Commerce Promotions and Adjustments using Illuminate Collections (Drupal 8)

Today I found another instance where I decided to use Illuminate Collections within my Drupal 8 code; whilst I was debugging an issue where a Drupal Commerce promotion was incorrectly being applied to an order.

No adjustments were showing in the Drupal UI for that order, so after some initial investigation and finding that $order->getAdjustments() was empty, I determined that I would need to get the adjustments from each order item within the order.

If the order were an array, this is how it would be structured in this situation:

$order = [
'id' => 1,
'items' => [
[
'id' => 1,
'adjustments' => [
['name' => 'Adjustment 1'],
['name' => 'Adjustment 2'],
['name' => 'Adjustment 3'],
]
],
[
'id' => 2,
'adjustments' => [
['name' => 'Adjustment 4'],
]
],
[
'id' => 3,
'adjustments' => [
['name' => 'Adjustment 5'],
['name' => 'Adjustment 6'],
]
],
],
];

Getting the order items

I started by using $order->getItems() to load the order's items, converted them into a Collection, and used the Collection's pipe() method and the dump() function provided by the Devel module to output the order items.

collect($order->getItems())
->pipe(function (Collection $collection) {
dump($collection);
});

Get the order item adjustments

Now we have a Collection of order items, for each item we need to get it's adjustments. We can do this with map(), then call getAdjustments() on the order item.

This would return a Collection of arrays, with each array containing it's own adjustments, so we can use flatten() to collapse all the adjustments into one single-dimensional array.

collect($order->getItems())
->map(function (OrderItem $order_item) {
return $order_item->getAdjustments();
})
->flatten(1);

There are a couple of refactors that we can do here though:

Use flatMap() to combine the flatten() and map() methods.

Use higher order messages to delegate straight to the getAdjustments() method on the order, rather than having to create a closure and call the method within it.

collect($order->getItems())
->flatMap->getAdjustments();

Filtering

In this scenario, each order item had three adjustments - the correct promotion, the incorrect one and the standard VAT addition. I wasn't concerned about the VAT adjustment for debugging, so I used filter() to remove it based on the result of the adjustment's getSourceId() method.

collect($order->getItems())
->flatMap->getAdjustments()
->filter(function (Adjustment $adjustment) {
return $adjustment->getSourceId() != 'vat';
});

Conclusion

Now I have just the relevant adjustments, I want to be able to load each one to load it and check it's conditions. To do this, I need just the source IDs.

Again, I can use a higher order message to directly call getSourceId() on the adjustment and return it's value to map().

collect($order->getItems())
->flatMap->getAdjustments()
->filter(function (Adjustment $adjustment) {
return $adjustment->getSourceId() != 'vat';
})
->map->getSourceId();

This returns a Collection containing just the relevant promotion IDs being applied to the order that I can use for debugging.

Now just to find out why the incorrect promotion was applying!