# Overview

Solidus can manage your store's inventory. This allows you to keep track of your current stock, backorder stock, as well as sold and shipped inventory. Because inventory touches orders, shipments, and the contents of your physical warehouse, there are many essential moving parts:

• Spree::InventoryUnit: Represents a stock item that has been sold. For more information, see Inventory units.
• Spree::StockItem: Counts the inventory for a specific Spree::Variant at a specific Spree::StockLocation. For more information, see Stock items.
• Spree::StockLocation: Represents a location where stock items are shipped from. Each stock location has Spree::StockItems for each variant in the store.
• Spree::StockMovement: Represents stock being moved from one Spree::StockLocation to another, or being added or removed from your store's inventory. For more information, see Stock movements.
• Spree::ReturnItem: Represents an inventory unit that is returned by a customer. For more information, see Return items.

# Turn off inventory tracking

If your store does not require inventory tracking, you can turn off the inventory system using Spree's application-wide configuration.

In your application's /config/initializers/spree.rb file, you can add your track_inventory_levels configuration to the main Spree::Config block:

# /config/initializers/spree.rb
Spree.config do |config|
  config.track_inventory_levels = false
end

# Inventory units

A Spree::InventoryUnit object is created every time that an item is sold. It tracks the state of the sold item. The state could be on_hand, backordered, shipped, or returned.

Inventory units associate each sold item with many other Solidus models. This includes the specific variant that was sold, an order, a line item, and a shipment.

# Stock management

Before a Spree::InventoryUnit is created, your store's stock is tracked using a number of stock management models. The following sections summarize the models and their functions in the stock management system.

# Stock items

On-hand inventory is tracked using the Spree::StockItem model. Each Spree::Variant in a store has a corresponding Spree::StockItem object with a count_on_hand value that represents the number of items you have in stock.

Note that if you have two stock locations, there are two Spree::StockItems for each variant in your store: one for each Spree::StockLocation. Each stock item counts the number of items in stock at a specific stock location.

# Stock movements

Whenever stock items are sold to customers, added to inventory, or removed from inventory, a new Spree::StockMovement object is created. The stock movement object documents how many items were added or removed.

Each Spree::StockMovement corresponds with a Spree::StockItem and how much the item's count_on_hand increases or decreases.

# Stock locations

A Spree::StockLocation represents a location where your inventory is shipped from. Each stock location has many Spree::StockItems and Spree::StockMovements.

Once a new stock location has been created, a new set of Spree::StockItems are created for it. The new set represents every Spree::Variant in your store.

# Stock transfers

If you manage multiple stock locations and inventory frequently moves between them, you may benefit from the solidus_stock_transfers extension. This extension adds a user interface for managing transfers in the solidus_backend.

# Return items

A Spree::ReturnItem is created for each inventory unit that a store administrator has included in a [return authorization][return-authorizations]. Once a return item is received back from the customer, it can be re-added to your on hand inventory.

Note that not all return items are resellable, as customer returns can be made for many reasons.

For more information, see the Returns documentation.