Why isn't my SubmitChanges() working in LINQ-t

问题:

I created a .MDF database in my WPF application.

I then generated LINQ-to-SQL classes and used LINQ get all the customers.

Then I run through them and change each of their last names.

However, when I call SubmitChanges, the database remains unchanged.

I thought that was the purpose of SubmitChanges(), to submit changes to the database?

What am I missing, how do I "submit changes" back to my database?

public Window1()
{
    InitializeComponent();

    Main2DataContext _db = new Main2DataContext();
    var customers = from c in _db.Customers
                    select c;

    foreach (var customer in customers)
    {
        customer.LastName = "CHANGED lastname"; //ListBox shows changes 
    }

    _db.SubmitChanges(); //does NOT save to database (???)

}

回答1:

I think I know what the problem is. Are you using a local .mdf file? If that's the case, check your bin/debug folder. I bet you have a database in there with the changes. I think you have an .mdf file in your project that is getting copied to the bin/debug folder everytime you build. Therefore the changes are getting saved to the copy, and you're not seeing it reflected in the copy that resides directly in your project.

回答2:

Make sure that your _db isn't getting reset to a new context at any point between the retrieval and change, if so well that is the problem. Also you can simplify your assignment of your datasource by doing TheListBox.ItemsSource = _db.Customers;. I have many places in current code where I am doing exactly what you describe and the changes are propogating fine. An additional suggestion, setup logging on your context (set the _db.Log to some writer, I generally use the Console.Out so I can watch changes in the output window while debugging) so you can see the changes that actually do occur when you call SubmitChanges().