Question

I’m writing a program that can be used by multiple users and concurrency is a big concern of mine. I wrote the program and didn’t even know about the subject, and now that I’m in multi-user testing, things are starting to blow up.

I want to be able to re-try the action if it fails, but don’t know how. My code shows a message box if there is an error, but what I’d really like to do is have it wait for a second and trigger the Button.Click() event again.

How can I accomplish this?

Button.Click()
{
    var Result = 
        from a in DB.Table
        where a.Id == 1
        select new {Row = a}.Single();

    Result.Row.Value = "hulkSMASH!!!";

    try
    {
        DB.SubmitChanges();
    }
    catch
    {
        MessageBox.Show("Action failed");
    }
}

Answer 1

You should read:

• How to: Manage Change Conflicts (LINQ to SQL)
• Optimistic Concurrency Overview (LINQ to SQL)

There are a bunch of links on those pages that should point you in the right direction. For example, the How to: Resolve Concurrency Conflicts by Overwriting Database Values link shows the following example code where you are in fact trying to submit the changes again in case it fails:

try
{
    db.SubmitChanges(ConflictMode.ContinueOnConflict);
}

catch (ChangeConflictException e)
{
    Console.WriteLine(e.Message);
    foreach (ObjectChangeConflict occ in db.ChangeConflicts)
    {
        //No database values are merged into current.
        occ.Resolve(RefreshMode.KeepCurrentValues);
    }
}

Take a look at the other links for more options, such as retaining database values or merging them.