# Inventory units

A Spree::InventoryUnit object is created every time that an item is sold. It tracks a sold item as it changes location: from being a sold item waiting in the warehouse to be shipped, to being a shipped item (or potentially a returned item).

Note that the Spree::InventoryUnit tracks an item as an object associated with a Spree::Order, a Spree::Shipment and a specific Spree::LineItem. This allows you to more closely track the status of an order and the line items and shipments associated with it.

A Spree::InventoryUnit object has the following attributes:

• state: The current state of the inventory unit. The state value can be on_hand, backordered, shipped, or returned.
• variant_id: The ID for the Spree::Variant corresponding with the inventory unit that has been sold.
• shipment_id: The ID for the Spree::Shipment that the inventory unit is being shipped in.
• pending: Documents whether the current unit is pending or finalized. If true, the stock for this unit has not yet been allocated to a shipment. If false, the stock has been finalized and is no longer tracked in the Spree::StockItem's count_on_hand value.
• line_item_id: The ID for the Spree::LineItem that the inventory unit corresponds with.
• carton_id: The ID for the Spree::Carton that the inventory unit belongs to.