Как реализовать добавление данных в MVVM C# WPF"?

Доброго времени суток!

Я изучаю MVVM и всю информацию я брал https://metanit.com/sharp/wpf/22.4.php

Я реализовал удаление данных, как показано в этом уроке, но добавление данных не работает, и это при том, что я использовал тот же способ, который показан в уроке.

Сам способ:

        private RelayCommand addCommand;
        public RelayCommand AddCommand
        {
            get
            {
                return addCommand ??
                  (addCommand = new RelayCommand(obj =>
                  {
                      Phone phone = new Phone();
                      Phones.Insert(0, phone);
                      SelectedPhone = phone;
                  }));
            }
        }

Пару слов о моей предметной области: есть таблица в базе данных Dish с колонками DishId, DishName, Cost, Weight.

Моя Model Dish:

class Dish : INotifyPropertyChanged
    {
        public Dish()
        {
            DishOrders = new List<DishOrder>();
        }

        private string dishName;
        private decimal cost;
        private short weight;

        [Key]
        public int DishId { get; set; }

        [MaxLength(20)]
        public string DishName
        {
            get { return dishName; }
            set
            {
                dishName = value;
                OnPropertyChanged();
            }
        }


        [Column(TypeName = "money")]
        public decimal Cost 
        { 
            get { return cost; } 
            set
            {
                cost = value;
                OnPropertyChanged();
            }
        }

        [Column(TypeName = "smallint")]
        public short Weight 
        {
            get { return weight; }
            set
            {
                weight = value;
                OnPropertyChanged();
            }
                
        }

        public ICollection<DishOrder> DishOrders;
 
        public event PropertyChangedEventHandler PropertyChanged;
        public void OnPropertyChanged([CallerMemberName] string prop = "")
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(prop));
        }
    }

Моя ViewModel:

class ApplicationViewModel : INotifyPropertyChanged
    {
        private CafeContext db;
        private Dish selectedDish;

        public IEnumerable<Dish> Dishes { get; set; }

        // команда добавления нового объекта
        private RelayCommand addCommand;
        public RelayCommand AddCommand
        {
            get
            {
                return addCommand ??
                  (addCommand = new RelayCommand(obj =>
                  {
                  }));
            }
        }

        private RelayCommand removeCommand;
        public RelayCommand RemoveCommand
        {
            get
            {
                return removeCommand ??
                  (removeCommand = new RelayCommand(obj =>
                  {
                      Dish dish = obj as Dish;
                      if (dish != null)
                      {
                          db.Dishes.Remove(dish);
                          db.SaveChanges();
                      }
                  },
                 obj => Dishes.Count() > 0));
            }
        }

        public Dish SelectedDish
        {
            get { return selectedDish; }
            set
            {
                selectedDish = value;
                OnPropertyChanged();
            }
        }

        public ApplicationViewModel()
        {
            db = new CafeContext();
            db.Dishes.Load();
            Dishes = db.Dishes.Local.ToBindingList();
        }

        public event PropertyChangedEventHandler PropertyChanged;
        public void OnPropertyChanged([CallerMemberName] string prop = "")
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(prop));
        }
    }

Мой View:

public partial class dish : Page
    {
        public dish()
        {
            InitializeComponent();

            DataContext = new ApplicationViewModel();
        }
    }

XAML-код:

<Page x:Class="cafe.Pages.dish"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
      xmlns:vm="clr-namespace:cafe.ViewModels"
      xmlns:local="clr-namespace:cafe.Pages"
      mc:Ignorable="d" 
      d:DataContext="{d:DesignInstance Type=vm:ApplicationViewModel}"
      d:DesignHeight="450" d:DesignWidth="800"
      Title="dish">

    <Grid>

        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="0.8*" />
        </Grid.ColumnDefinitions>

        <ListBox Grid.Column="0" ItemsSource="{Binding Dishes}"
                 SelectedItem="{Binding SelectedDish}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Margin="5">
                        <TextBlock FontSize="18" Text="{Binding Path=DishName}" />
                        <TextBlock Text="{Binding Path=Cost}" />
                        <TextBlock Text="{Binding Path=Weight}" />
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

        <StackPanel Grid.Column="1" Orientation="Horizontal">
            <Button Command="{Binding AddCommand}" Margin="0,275,0,110" Width="80" Content="+">
            </Button>
            <Button Command="{Binding RemoveCommand}" 
                    CommandParameter="{Binding SelectedDish}" Margin="0,275,0,110" Width="80" Content="-">
            </Button>
        </StackPanel>

        <StackPanel Grid.Column="1" DataContext="{Binding SelectedDish}">
            <TextBlock Text="Блюдо" />
            <TextBox Text="{Binding DishName, UpdateSourceTrigger=PropertyChanged}" />
            <TextBlock Text="Цена" />
            <TextBox Text="{Binding Cost, UpdateSourceTrigger=PropertyChanged}" />
            <TextBlock Text="Вес" />
            <TextBox Text="{Binding Weight, UpdateSourceTrigger=PropertyChanged}" />
        </StackPanel>
    </Grid>
</Page>