This value is a string to allow use of non-numeric, unique tracking numbers assigned by a shipping company to be applied to an order. It is present in the Basket, OrderTemplate, and PurchaseOrder classes so that it can be set as part of pre-checkout processing of a basket if a tracking number is known prior to conversion of a basket to a placed purchase order. This property value defaults to nullNothingnullptra null reference (Nothing in Visual Basic) at creation of a basket or order template; if it is still nullNothingnullptra null reference (Nothing in Visual Basic) when a basket is converted to a purchase order (using SaveAsOrder), a new, unique 64-bit integer value will be generated, converted to a string, and placed in this property, so that the uniqueness characteristics of this field are upheld when saving the purchase order.
The string value provided to the setter is trimmed prior to use.
The default maximum length for TrackingNumber is 32 characters, as defined in the corresponding table column constraint specified in the default orders storage mapping file, OrderObjectMappings.xml.