The UpdateInventory message extends the CommerceMessage class. It adds one property:
itemIds– a list of IDs of items that were previously unavailable (BACKORDERABLE, PREORDERABLE, or OUT_OF_STOCK) but now have stock available.
UpdateInventory is sent by a third-party system, such as an inventory subsystem, to indicate that items are available. The HardgoodFulfiller in Core Commerce listens for these messages. The HardgoodFulfiller queries the order repository for all shipping groups that contain items from the list that are in a preordered or backordered state.
