Add Inventory events for developers to hook into

[engram-design]

This is in relation to the Back in Stock plugin, but I'm sure there's a general need for this. There seems to be no events raised when handling inventory items.

Previously, as stock was managed at the Variant level, listening to Variant::EVENT_BEFORE_SAVE was a straightforward way to know about stock changes. However, as stock is now managed as dedicated inventory, we should be listening to the stock level changes on that, for our plugin to be able to notify users that a variant's stock has been added and is available for sale.

I would propose the usual update/delete events, similar to other models.

[lukeholder]

Agree we should have some more events in inventory system.

We should add an event to the Purchasables::updateStoreStockCache() method which would allow you to listen to the level per store after any inventory movement or inventory update job is executed.

I can put it on the list but PR is welcome with the event at the end of this method.

commerce/src/services/Purchasables.php

Lines 215 to 236 in efd03a9

	public function updateStoreStockCache(Purchasable $purchasable, bool $allSites = false): void
	{
	if ($allSites) {
	$purchasables = $purchasable::find()
	->siteId('*')
	->id($purchasable->id)
	->status(null)->all();
	} else {
	$purchasables = [$purchasable];
	}
	/** @var Purchasable $purchasable */
	foreach ($purchasables as $purchasable) {
	$stock = Plugin::getInstance()->getInventory()->getInventoryLevelsForPurchasable($purchasable)->sum('availableTotal');
	Craft::$app->getDb()->createCommand()
	->update(
	table: Table::PURCHASABLES_STORES,
	columns: ['stock' => $stock],
	condition: ['purchasableId' => $purchasable->id, 'storeId' => $purchasable->getStore()->id])
	->execute();
	}

[lukeholder]

@bjerringgaard What are you looking to be able to hook into?

Any use cases?

[bjerringgaard]

@lukeholder
I would like the event to be triggered when the inventory item qty is either adjusted or set (previously used the Variant::before_save)
the event should include: the new stock value, the old stock value, and adjustment type (SET, ADJUST)

I have a couple of client webshops where this would be useful for:

• Back in stock emails (When stock is updated fra 0 to something else)
• Low stock warning emails (Letting the inventory manager get an email, when an item is due for reordering)
• Shop running custom tables with additional product data, where this would improve the ease of cache clearing
• Webshop running 3rd party WMS / ERP, where this event would be ideal for sending confirmation webhooks etc.

[lukeholder]

Thanks for that. I will look into adding events, but most likely they will be read-only and not designed for modifying the actual stock change at runtime. Would this be ok?

[bjerringgaard]

Readonly would be just fine.
Just need them for triggering other events in the system.

[lukeholder]

@bjerringgaard #4063 Added these events for a future 5.5

[lukeholder]

These events now exist in 5.5: #4063