Today I found another instance where I decided to use [Illuminate Collections][0] within my Drupal 8 code; whilst I was debugging an issue where a [Drupal Commerce][1] 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:
```php
$order = [
'id' => 1,
'items' => [
[
'id' => 1,
'adjustments' => [
['name' => 'Adjustment 1'],
['name' => 'Adjustment 2'],
['name' => 'Adjustment 3'],
]
],
[
'id' => 2,
'adjustments' => [
['name' => 'Adjustment 4'],
]
],
[
'id' => 3,
'adjustments' => [
['name' => 'Adjustment 5'],
['name' => 'Adjustment 6'],
]
],
],
];
```
## Getting the order items
I started by using `$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][2] to output the order items.
```php
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.
```php
collect($order->getItems())
->map(function (OrderItem $order_item) {
return $order_item->getAdjustments();
})
->flatten(1);
```
There are a couple of refactors that we can do here though:
- Use `flatMap()` to comine the `flatten()` and `map()` methods.
- Use [higher order messages][3] to delegate straight to the `getAdjustments()` method on the order, rather than having to create a closure and call the method within it.
```php
collect($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.
```php
collect($order->getItems())
->flatMap->getAdjustments()
->filter(function (Adjustment $adjustment) {
return $adjustment->getSourceId() != 'vat';
});
```
## Conclusion
Now I have just the relevant adjustments, I want to be able to load each one to load it and check it’s conditions. To do this, I need just the source IDs.
Again, I can use a higher order message to directly call `getSourceId()` on the adjustment and return it’s value to `map()`.
```php
collect($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!
