Question

Ok, I am total newbie so bear with me.
Trying to implement an ordering system and wish
to save the orders to the database with LINQ to Entities. I can do it now
but for each new object that is saved to the orders table
a new row is inserted, with new OrderNo for each ProductID where as I obviously
should be able to have multiple ProductID’s for each OrderNo.

Everything is very simplified as I am just testing.

I have an orders table with columns as such:

OrderNo PK, Identity specification
Line int PL
ProductID int

and a products table

ProductID int PK

An order entity object is instantiated and its properties
are populated with data from a form which is posted to an action method.
It is then saved to the orders table with the following code:

(DropDownList1Value) has value of an existing ProductID and “DropDownList1Value” is the id of the DropDownList element in view.

[HttpPost]
public ActionResult OrderProcessor()
{            
    int productId = int.Parse(Request.Form["DropDownList1Value"]);
    var order = new Order(); 
    order.ProductID = productId;
    context.Orders.AddObject(order);           
    context.SaveChanges();            
    return View(order);
}

So the records that are inserted look as such:
Sorry, couldn’t line up the values under their respective column name in this editor.

OrderNo Line ProductID

101     0    3
102     0    5
103     0    2

Where as I want something like this:

OrderNo  Line ProductID

101      1    3
101      2    5
101      3    2
102      1    2

So I wish to know how can I modify the orders table so it
can have multiple records with same “OrderNo” and just increment for “Line” for diff ProductID’s and how do I go about inserting such records with LinQ to Entities where
I will obviously have many ProductId from multiple DropDowLists
and they will all be for the one order.

Currently I have foreign key dependency on ProductID in Products table,
so no record in the Orders table can have ProductID which does not exists in the Products table.
I need to make the table depend on the whole key that is OrderNo + Line
and have the “Line” auto increment.

Or is there a much better way of implementing of what I am after here?

Thanks.

Answer 1

Let me first explain briefly what I understood.

There is an invoice, which contains several products for one order number.
and this is how your invoice looks like:

Order Number: 101
------------------
Sl.       Products
1         3
2         5
3         2

Before answering I want to point out that you are taking OrderId from a form (That is from client side) This is a wrong and INSECURE approach. Let the order id be AutoGenerated by database.

I would suggest to tweak your database design a little.
Here is a solution that will work.
Note: I am consedering your database support Auto-Increment, for MS SQL replace it with IDENTITY, for Oracle you need to create a sequence.

Product (
     id        INT   PK  AUTO-INCREMENT
);

Order (
     id        INT   PK  AUTO-INCREMENT
     user-id   INT   FK                      # user who purchased
     ### and other common details Like date of purchase etc.
);

Order-Detail (
     id         INT   PK  AUTO-INCREMENT
     order-id   INT   FK                     # Common order id
     pdt-id     INT   FK                     # product which was purchased.
);

When you make a purchase:
1. Insert a row in order table
2. Fetch the last inserted id
3. Insert order-id from last step and products which are purchased in Order-Detail table,

Fetch all the orders made by a user:
1. Read from order table.

Fetch all products purchased for an order:
1. Fetch details from Order-Detail
Note: You will get List of products purchased, Use Order-detail.id as “Line”

EDIT:
Thanx to HLGEM’s comment
If you think price of a product may change then instead of updating the price add a new row to the table (and flag the old table so that it wont be visible, you can also have a column in new table pointing to old table), thus old purchase will point to old product and new orders will point to updated (new) row.

There is one more approach this problem:
store the current cost of product in order-detail table.

If you are facing difficulty understanding above solution here is another and simpler one.
In Order table, Make a composite primary key including OrderNo and Line.
Whenever inserting into database you will need to generate line number in your code, which you can do by runnign a loop over array of propduct being purchased.