To modify an Order, you must supply either a CatalogRefId of a CommerceItem or a ShippingGroupCommerceItemRelationship ID. It is recommended that you modify an Order by ShippingGroupCommerceItemRelationship ID, especially if you intend to support complex product-SKU relationships, such as multiple CommerceItems with the same catalogRefId (SKU ID) or multiple shipping groups. For example, a customer could order 5 of a given item and choose to ship a quantity of 3 to a home address and the remaining 2 to a work address. In this example, to remove the items being shipped to the work address, you would modify (and ultimately remove) the ShippingGroupCommerceItemRelationship instead of modifying the CommerceItem.
The following subsections describe both order modification methods:
