PurchaseOrderChangedEvent.cs

public class PurchaseOrderChanges
{    
    // other attributes not relevant for this
    PurchaseOrderLineChange[] PurchaseOrderLineChanges;
}

public class PurchaseOrderLineChange
{
    int PurchaseOrderLineId;
    int? QuantityCancelled;
    DateTime? ExpectedDeliveryDate;
    int ResultingVersion;
}