MDF table content is deleted when starting application from within VS

Question

Very mysterious issue here.

I have mdf-file in project with single table (double-clicking will show this):

CREATE TABLE [dbo].[Table] (
    [Id]      DATETIME        NOT NULL,
    [Version] NCHAR (20)      NULL,
    PRIMARY KEY CLUSTERED ([Id] ASC)
);

Then I add dbml (Linq-to-SQL), drag table there, add some code

partial class TestDataContext
{
    public static string DatabaseFile { get; private set; }
    public static string ConnectionString { get; private set; }

    static TestDataContext()
    {
        DatabaseFile = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Test.mdf");
        ConnectionString = string.Format(@"Data Source=(LocalDB)\v11.0;AttachDbFilename={0};Integrated Security=True", DatabaseFile);
    }

    public TestDataContext Attach()
    {
        Detach();
        var context = new TestDataContext(ConnectionString);
        // re-create database
        if (!context.DatabaseExists() && !File.Exists(DatabaseFile))
            context.CreateDatabase();
        return context;
    }

    public static void Detach()
    {
        try
        {
            using (var master = new DataContext(@"Data Source=(LocalDB)\v11.0;Initial Catalog=master;Integrated Security=True"))
            {
                master.ExecuteCommand(string.Format(@"ALTER DATABASE [{0}] SET OFFLINE WITH ROLLBACK IMMEDIATE", DatabaseFile));
                master.ExecuteCommand(string.Format(@"exec sp_detach_db '{0}'", DatabaseFile));
            }
        }
        catch { } // should be safe
    }

    public void Test()
    {
        var row = new Table() { Id = DateTime.Now, Version = "test1.0" };
        Tables.InsertOnSubmit(row);
        System.Threading.Thread.Sleep(5);
        row = new Table() { Id = DateTime.Now, Version = "test1.1" };
        Tables.InsertOnSubmit(row);
        SubmitChanges();
    }
}

It's all needed to detach database and to re-create database if file is deleted (maybe it's related to issue, see further). That new database is created near exe-file (don't mix it with one in project, used only to define structure and generate dmbl).

Now the problem: when I run application from within VS (F5), then this table is always blank. Even before calling Attach() its content from previous run is erased ! It looks like if VS opens new mdf-file, find my table there (lol) and clears it!

Most confusing part: if compiled exe-file is running directly, then content persist between launches (as intended). As soon as I hit F5 in VS .. it become empty again.

Any idea?

---

I open that new mdf-file in VS "Database Explorer", to be able to see what is going on. Application adds some rows by calling Test() and I see that in application and in explorer. Then application exits. Data still. Yes, I click refresh button, it is still. Then I hit F5 and before pressing button which call Attach() switch to explorer and hit refresh there.. table is empty.

Answer 1

Is the MDF file in your solution? Check the file properties for the 'Copy to Output Directory'. It should be on "Do not copy"