在Windows Phone的SQL Server Compact工具3.5中添加新列时出错

Question

I have a database consist of 3 column which are Id(int), Title(nvarchar) and Description(nvarchar). I added a new column name more(nvarchar) and generated a new database context to replace the old one. I am not able to run my application after adding a new column. What am I missing? Thanks

Below is the error message:

A first chance exception of type 'System.Data.SqlServerCe.SqlCeException' occurred in Microsoft.Phone.Data.Internal.ni.dll

Extra: After removing the new column more(nvarchar), and regenerated a new database context to replace it again, it works as normal. Meaning its back as the old one without adding a new column to the table.

Below is some code for the MainPage.xaml.cs:

namespace PhoneApp
{
public partial class MainPage : PhoneApplicationPage
{
    // Constructor
    public MainPage()
    {
        InitializeComponent();

        // Set the data context of the LongListSelector control to the sample data
        DataContext = App.ViewModel;

        // Sample code to localize the ApplicationBar
        //BuildLocalizedApplicationBar();
    }

    // Load data for the ViewModel Items
    protected override void OnNavigatedTo(NavigationEventArgs e)
    {
        if (!App.ViewModel.IsDataLoaded)
        {
            App.ViewModel.LoadData();
        }

        using (DatabaseContext c = new DatabaseContext(DatabaseContext.ConnectionString))
        {
            c.CreateIfNotExists();
            c.LogDebug = true;
            //output todolist data from database
            MLongListSelector.ItemsSource = c.ToDoList.ToList();
        }
    }

    // Handle selection changed on LongListSelector
    private void MainLongListSelector_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {

        // If selected item is null (no selection) do nothing
        if (MLongListSelector.SelectedItem == null)
            return;

        //select the item selected from the class.property
        var title = (MLongListSelector.SelectedItem as PhoneApp.ToDoList).Title;
        var desc = (MLongListSelector.SelectedItem as PhoneApp.ToDoList).Description;
        var id = (MLongListSelector.SelectedItem as PhoneApp.ToDoList).Id;

        //send data through Title and Desc
        NavigationService.Navigate(new Uri("/ToDoDetailPage.xaml?Title=" + title + "&Desc=" + desc + "&Id=" + id, UriKind.Relative));


        // Navigate to the new page
        //NavigationService.Navigate(new Uri("/ToDoDetailPage.xaml", UriKind.Relative));

        // Reset selected item to null (no selection)
        MLongListSelector.SelectedItem = null;
    }

   private void LongListSelector_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        var si = MainLongListSelector.SelectedItem as PhoneApp.ViewModels.ItemViewModel;

        if (MainLongListSelector.SelectedItem == null)
            return;

        if (si.LineOne.Equals("+ To Do List"))
            NavigationService.Navigate(new Uri("/todolistPage.xaml", UriKind.Relative));
        else if (si.LineOne.Equals("+ Reminder"))
            NavigationService.Navigate(new Uri("/reminderPage.xaml", UriKind.Relative));

        // Reset selected item to null (no selection)(//important)
        MainLongListSelector.SelectedItem = null;
    }

}
}

Answer 1

I ran into a similar issue. As far as I could tell the issue is attempting to modify the schema against an existing database. In my case the code does not initialize the DB if it already exists.

if (db.DatabaseExists() == false)
{
    // Create database.
    db.CreateDatabase();
}

...so the schema changes were not reflected, resulting in a null reference when selecting the new column. I resolved by restarting the phone emulator which removed the previous db file.