Trouble With Calculated Columns

I have an OrderDetails table, ShipHeader table and a ShipDetails table in my database. I am trying to add a couple of columns to my OrderDetails table. I need two additional columns in my OrderDetails that are calculated. One should be called "Shipped" and give me the sum of all the ship Qty records for theat line item. The other should be called "Returned" and do the same for the return records. I was able to create this in a View without a problem. However, I need a method of creating this table that will still allow me to edit the information in the other columns in the OrderDetail table while viewing the shipped and returned information for each line item. With a View, I cannot edit any of the information while viewing it. Should I use a function? A stored procedure? If so, how do I code this? The tables are listed below.


CREATE TABLE OrderHeader
(
OrderID int identity primary key,
Status int,
StartDate datetime,
EndDate datetime
)--Use Type 1 = "Quote" Type 2 = "Cancelled" Type 3 = "Confirmed", Type 4 = "Shipped", Type 5 = "Part Shipped", Type 6 = "Part Returned", Type 7 = "Returned, Type 8 = "Mixed"
CREATE TABLE OrderDetail
(
OrderDetailID int identity primary key,
OrderID int FOREIGN KEY REFERENCES OrderHeader(OrderID),
ItemName varchar(30),
Qty int,
SiteID int,
)
CREATE TABLE ShipHeader
(
ShippingID int identity primary key,
Type int,
SiteID int,
ActionDate datetime
)--Use Type 1 = "Ship" Type 2 = "Return" Type 3 = "Lost"
CREATE TABLE ShipDetail
(
ShipDetailID int identity primary key,
ShippingID int NOT NULL FOREIGN KEY REFERENCES ShipHeader(ShippingID),
OrderDetailID int,
Qty int
)