# Stock movements

A Spree::StockMovement object is created every time that a stock item moves in or out of a stock location. This objects documents how many items were added or removed.

The Spree::StockMovement model has the following attributes:

• stock_item_id: The ID of the Spree::StockItem the movement is related to.
• quantity: The amount of stock items added or removed from the Spree::StockItem's count_on_hand value.
• originator_type and originator_id: The model and ID of an object that initiated the creation of the current stock movement. For example, an originator could be an administrator (a Spree::User) adding new stock or a Spree::Shipment being created after an order is placed.

# Usage example

A typical example of a stock movement would be when a customer buys an item from your store:

1. A stock item has a count_on_hand value of 20.
2. A customer buys one unit of its associated variant.
3. A new Spree::StockMovement object is created.
   • It has a quantity of -1.
   • It has a originator_type of Spree::Shipment because a new shipment triggered the movement.
4. The stock item's count_on_hand value is updated to 19.

# Administrating inventory

Administrators can generate stock movements by changing the "Count On Hand" value for a stock item in the solidus_backend (on the Stock page). However, they cannot create a stock movement directly.

Because of this, Solidus has no concept of adding to existing inventory. For example:

• A stock item has a count_on_hand value of 7.
• A store administrator receives 25 new items to add to inventory.
• They log into the backend and change the count on hand from 7 to 33.
• This creates a new Spree::StockMovement with a quantity of 25. (7 + 25 = 33.)

If an administrator does not account for the units already in stock, they may enter the wrong value into the "Count On Hand" field for an item.

For example, if the administrator changes the value from 7 to 25, then the stock movement only documents that 18 units were added to inventory. (7 + 18 = 25.)