Database Utilities

Whereas DataContext enables you to create and delete a database file, a custom class, called DatabaseUtility, is used to directly create and delete the database in isolated storage and to build the connection string for the database.

TwitterDatabaseUtility extends the DatabaseUtility class, providing the default database filename. TwitterDatabaseUtility is used in various locations to create a DataContext for the Twitter database.

DatabaseUtility includes an InitializeDatabase method that creates the isolated storage file for the database. When it is called, if the wipe parameter is true and the database already exists, it is deleted before being re-created. See the following excerpt:

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public void InitializeDatabase(DataContext dataContext, bool wipe = false)
{
    ArgumentValidator.AssertNotNull(dataContext, "dataContext");

    if (localDatabaseMode != LocalDatabaseMode.ReadWrite
        && localDatabaseMode != LocalDatabaseMode.Exclusive)
    {
        return;
    }

    if (wipe && dataContext.DatabaseExists())
    {
        dataContext.DeleteDatabase();
    }

    if (!dataContext.DatabaseExists())
    {
        dataContext.CreateDatabase();
    }
}

Initialization of the local database occurs when the Launching event of the PhoneApplicationService is raised. For testing purposes, if a debugger is attached, the database is deleted so as to begin with a clean slate. The following excerpt shows the Launching event handler:

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void Application_Launching(object sender, LaunchingEventArgs e)
{
    Debug.WriteLine("Application Launching");

    StateManager.Initialize();

    /* For the Twitter demo. */
    var twitterDatabaseUtility = new TwitterDatabaseUtility();
    bool wipeDatabase = Debugger.IsAttached;
    twitterDatabaseUtility.InitializeDatabase(wipeDatabase);
}

When the app is launched, the handler ensures that the database file is created in isolated storage.