fix-2 sqlalchemy exception

database.py

@@ -297,6 +297,7 @@ class OrderItem(DeferredReflection, TableDeclarativeBase):
     product = relationship("Product")
     # The order in which this item is being purchased
     order_id = Column(Integer, ForeignKey("orders.order_id"), nullable=False)
+    order = relationship("Order")
 
     # Extra table parameters
     __tablename__ = "orderitems"

worker.py

@@ -652,7 +652,7 @@ class Worker(threading.Thread):
             # Create {quantity} new OrderItems
             for i in range(0, cart[product][1]):
                 order_item = db.OrderItem(product=cart[product][0],
-                                          order_id=order.order_id)
+                                          order=order)
                 self.session.add(order_item)
         # Ensure the user has enough credit to make the purchase
         credit_required = self.__get_cart_value(cart) - self.user.credit