Question

In my Windows Phone Mango app, I have a bunch of checkboxes, each corresponding to a day of the week. I want to filter the data I query by which checkboxes are checked. Here’s what I’ve come up with, but I feel like there’s a better solution:

Declare the checkboxes in XAML:

            <CheckBox Content="Mon" x:Name="MonCheckbox" Checked="DayCheckbox_Tap" Unchecked="DayCheckbox_Tap"/>
            <CheckBox Content="Tue" x:Name="TueCheckbox" Grid.Column="1" Checked="DayCheckbox_Tap" Unchecked="DayCheckbox_Tap" />
            <CheckBox Content="Wed" x:Name="WedCheckbox" Grid.Column="2" Checked="DayCheckbox_Tap" Unchecked="DayCheckbox_Tap" />
            <CheckBox Content="Thur" x:Name="ThurCheckbox"  Grid.Row="1" Checked="DayCheckbox_Tap" Unchecked="DayCheckbox_Tap" />
            <CheckBox Content="Fri" x:Name="FriCheckbox" Grid.Row="1" Grid.Column="1" Checked="DayCheckbox_Tap" Unchecked="DayCheckbox_Tap" />
            <CheckBox Content="Sat" x:Name="SatCheckbox" Grid.Row="1" Grid.Column="2" Checked="DayCheckbox_Tap" Unchecked="DayCheckbox_Tap" />
            <CheckBox Content="Sun" x:Name="SunCheckbox" Grid.Row="2" Grid.Column="0" Checked="DayCheckbox_Tap" Unchecked="DayCheckbox_Tap" />

Associate a day with each checkbox:

    public MainPage()
    {
        InitializeComponent();

        LayoutRoot.DataContext = this;

        // This is grossly imperative. Can it be done in XAML?
        MonCheckbox.Tag = DayOfWeek.Monday;
        TueCheckbox.Tag = DayOfWeek.Tuesday;
        WedCheckbox.Tag = DayOfWeek.Wednesday;
        ThurCheckbox.Tag = DayOfWeek.Thursday;
        FriCheckbox.Tag = DayOfWeek.Friday;
        SatCheckbox.Tag = DayOfWeek.Saturday;
        SunCheckbox.Tag = DayOfWeek.Sunday;

        // ...
    }

Maintain a collection of the currently selected days:

    ICollection<DayOfWeek> _selectedDays = new Collection<DayOfWeek>();

    private void DayCheckbox_Tap(object sender, RoutedEventArgs e)
    {
        CheckBox checkbox = (CheckBox)sender;
        if (_selectedDays.Contains((DayOfWeek)checkbox.Tag))
        {
            _selectedDays.Remove((DayOfWeek)checkbox.Tag);
        }
        else
        {
            _selectedDays.Add((DayOfWeek)checkbox.Tag);
        }

        refreshCheckinData();
    }

The problem comes when I go to refresh the data that’s displayed to the user:

    private void refreshCheckinData()
    {
        Checkins.Clear();
        Checkins.AddAll(from checkin in checkinData.Items
                        where _selectedDays.Contains(checkin.DateTime.DayOfWeek)
                        select checkin);
    }

public static class ExtensionMethods
{
    public static void AddAll<T>(this ICollection<T> dest, IEnumerable<T> source)
    {
        if (dest == null)
        {
            throw new ArgumentNullException("dest");
        }

        foreach (T t in source)
        {
            dest.Add(t);
        }
    }
}

When the code tries to iterate over source in AddAll(), the following exception occurs:

Method 'Boolean Contains(System.DayOfWeek)' has no supported translation to SQL."   System.Exception {System.NotSupportedException}

How can I get around this? Why does Contains require a SQL translation? Is there a better approach to this whole thing, using more declarative XAML and less imperative code-behind?

Update: I tried changing the query to:

where _selectedDays.Any(day => day == checkin.DateTime.DayOfWeek)

now I get the following error:

"Local sequence cannot be used in LINQ to SQL implementations of query operators except the Contains operator." System.Exception {System.NotSupportedException}

_selectedDays is defined in memory. why does it need to be translated to SQL?

Answer 1

Your original query is close. I think the Contains() method on ICollection is getting in the way of the SQL translator — I would need to double check the code to be sure.

You can work around this by forcing selection of the Enumerable.Contains() extension method by changing your code to this:

    private void refreshCheckinData()
{
    Checkins.Clear();
    Checkins.AddAll(from checkin in checkinData.Items
                    where _selectedDays.AsEnumerable().Contains(checkin.DateTime.DayOfWeek)
                    select checkin);
}

Enumerable.Contains(T) extension method will translate into an IN clause in the database.

The resulting query will be something like this:
SELECT [t0].[Key], [t0].[Day]
FROM [Stuff] AS [t0]
WHERE [t0].[Day] IN (@p0, @p1)