<DataGrid x:Name="filmDataGrid" AutoGenerateColumns="False" Grid.ColumnSpan="2" EnableRowVirtualization="True" ItemsSource="{Binding Source={StaticResource filmViewSource}}" Margin="25,18,593,153" RowDetailsVisibilityMode="VisibleWhenSelected">
                        <DataGrid.Columns>
                            <DataGridTextColumn x:Name="filmIdColumn2" Binding="{Binding FilmId}" Header="Film Id" Width="SizeToHeader"/>
                            <DataGridTextColumn x:Name="titleColumn" Binding="{Binding Title}" Header="Title" Width="110"/>
                            <DataGridTextColumn x:Name="lengthColumn" Binding="{Binding Length}" Header="Length" Width="70"/>
                            <DataGridTemplateColumn x:Name="premiereDateColumn" Header="Premiere Date" Width="110">
                                <DataGridTemplateColumn.CellTemplate>
                                    <DataTemplate>
                                        <DatePicker SelectedDate="{Binding PremiereDate, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}"/>
                                    </DataTemplate>
                                </DataGridTemplateColumn.CellTemplate>
                            </DataGridTemplateColumn>
                        </DataGrid.Columns>
</DataGrid>

<Button Content="Save" Grid.Column="1" HorizontalAlignment="Left" Margin="10,262,0,0" VerticalAlignment="Top" Width="82" Height="25" Click="Button_Click_2"/>

MyContext _context = new MyContext();
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {

            System.Windows.Data.CollectionViewSource screeningViewSource = ((System.Windows.Data.CollectionViewSource)(this.FindResource("screeningViewSource")));
            _context.Screenings.Load();
            screeningViewSource.Source = _context.Screenings.Local.ToBindingList();

            System.Windows.Data.CollectionViewSource filmViewSource = ((System.Windows.Data.CollectionViewSource)(this.FindResource("filmViewSource")));
            _context.Films.Load();
            filmViewSource.Source = _context.Films.Local.ToBindingList();

            System.Windows.Data.CollectionViewSource hallViewSource = ((System.Windows.Data.CollectionViewSource)(this.FindResource("hallViewSource")));
            _context.Halls.Load();
            hallViewSource.Source = _context.Halls.Local.ToBindingList();

            System.Windows.Data.CollectionViewSource customerViewSource = ((System.Windows.Data.CollectionViewSource)(this.FindResource("customerViewSource")));
            _context.Customers.Load();
            customerViewSource.Source = _context.Customers.Local.ToBindingList();

        }


        private void Button_Click_1(object sender, RoutedEventArgs e)
        {
            _context.SaveChanges();
        }

public class Film
    {
        [Key]
        public int FilmId { get; set; }
        [MaxLength(40)]
        public string Title { get; set; }
        public float Length { get; set; }
        public string Description { get; set; }
        public DateTime PremiereDate { get; set; }
        public byte[] Picture { get; set; }

    }
  public class MyContext : DbContext
    {
        public MyContext() : base("MyContext")
        {
            Database.Log = Console.Write;
        }
        public DbSet<Film> Films { get; set; }

    }

System.Data.Entity.Validation.DbUnexpectedValidationException: „An unexpected exception was thrown during validation of 'Screenings' when invoking System.ComponentModel.DataAnnotations.MaxLengthAttribute.IsValid. See the inner exception for details.”


InvalidCastException: Unable to cast object 'System.Collections.Generic.HashSet`1[db1.Screening]' to  'System.Array'.