实体框架：更新连接表

Question

I have following table setup:

• Order (ID)
• Product (ID) [where ProductID 1 and 2 already exist]
• OrderProduct (OrderId, ProductID) [two keys FK'ng to Order and Product tables]

And I'am trying to add a record to Order table assigning 2 products in to the order as follows:

var order = new Order();
order.Products.Add(new Product {ID=1});
order.Products.Add(new Product {ID=2});

db.SaveChanges();

The problem is: When saving the order, two Products are getting inserted in to the DB, instead of referring to the product records that already exists.

Please help. Thanks.

Answer 1

You should use db instead of creating new Product, like in this example:

var order = new Order();
order.Products.Add(db.Products.First(p => p.ID = 1));
order.Products.Add(db.Products.First(p => p.ID = 2));

db.SaveChanges();

Or, you need to "Update Reference" after product creation. you can do something like this:

var product = new Product() { ID = 1 };
db.Attach(product);
order.Products.Add(product);