I am getting the following error when I attempt to add something to my database.

System.InvalidOperationException: ‘The instance of entity type ‘IngredientCategory’ cannot be tracked because another instance with the key value ‘{Id: 15}’ is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.’

This is the line that throws the error in the view model:

context.Ingredients.Add(newItem);

View Model

public partial class IngredientViewModel: ObservableObject
{

RecipeDBContext context;

private Ingredient _ingredient = new Ingredient();
public Ingredient Ingredient => _ingredient;

[ObservableProperty]
private ObservableCollection<Ingredient> _ingredients;
public List<IngredientCategory> Categories { get; set; }

public IngredientViewModel()
{
    context = new RecipeDBContext();            
    _ingredients = new ObservableCollection<Ingredient>();
    UpdateIngredients(context.Ingredients.ToList());
    _ingredients.CollectionChanged += this.OnCollectionChanged;
    Categories= context.IngredientCategories.Where(p => p.ParentId != null).ToList();    
}

public void UpdateIngredients(List<Ingredient> ingredients)
{
    Ingredients.Clear();    
    foreach (Ingredient ingredient in ingredients)
    {       
        Ingredients.Add(ingredient);
    }
}

void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{        
    if (e.NewItems != null)
    {
        
        foreach (Ingredient newItem in e.NewItems)
        {           
            context.Ingredients.Add(newItem);
        }        
    }

    if (e.OldItems != null)
    {
        foreach (Ingredient oldItem in e.OldItems)
        {            
            context.Ingredients.Remove(oldItem);                        
        }
    }
    context.SaveChanges();
}
}

Xaml

<?xml version="1.0" encoding="utf-8"?>
<ContentDialog
    x:Class="RecipeApp.Views.Dialogs.AddIngredientDialog"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:RecipeApp.Views.Dialogs"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    xmlns:models="using:RecipeApp.Models" d:DataContext="{d:DesignInstance Type=models:Supplier}"
    xmlns:viewModels="using:RecipeApp.ViewModels" 
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
    Title="Save your work?"
    PrimaryButtonText="Save"    
    CloseButtonText="Cancel"
    DefaultButton="Primary"
    Width="1000"
    Height="1000">

    <ContentDialog.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="/Resources/FormUI.xaml"/>
            </ResourceDictionary.MergedDictionaries>
            <Style TargetType="TextBox"  x:Key="ValidatedTextBox2">
                <Setter Property="FontSize"
            Value="50" />
            </Style>
        </ResourceDictionary>
    </ContentDialog.Resources>

    <StackPanel>
        <TextBox x:Name="NameTextBox" Header="Name" PlaceholderText="Enter Name" PlaceholderForeground="Gray"  IsColorFontEnabled="True" Text="{x:Bind ViewModel.Ingredient.Name, Mode=TwoWay}" IsSpellCheckEnabled="True"/>
        <TextBox x:Name="DescTextBox" TextWrapping="Wrap"  AcceptsReturn="True" SelectionHighlightColor="Green" MinWidth="400" Width="600" Height="300" IsSpellCheckEnabled="True" Text="{x:Bind ViewModel.Ingredient.Description, Mode=TwoWay}"/>
        <ComboBox x:Name="ingredientCategoryBox" ItemsSource="{x:Bind ViewModel.Categories}" SelectionChanged="ingredientCategoryBox_SelectionChanged">
            <ComboBox.ItemTemplate>
                <DataTemplate x:DataType="models:IngredientCategory">
                    <StackPanel Orientation="Horizontal">
                        <TextBlock Text="{x:Bind Name}" />
                    </StackPanel>
                </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>
        <StackPanel Visibility="{x:Bind ViewModel.Ingredient.HasErrors, Mode=OneWay}" Grid.Row="7" Grid.Column="0" Grid.ColumnSpan="2" Orientation="Vertical" Margin="0 50 0 0">
            <TextBlock FontSize="20">Errors:</TextBlock>
            <Border Background="Gray">
                <TextBlock x:Name="ErrorsBox"  Text="{x:Bind ViewModel.Ingredient.Errors, Mode=OneWay}" Foreground="White"/>
            </Border>
        </StackPanel>
    </StackPanel>
</ContentDialog>

Code behind file

public sealed partial class AddIngredientDialog : ContentDialog
{    
    public IngredientViewModel ViewModel { get; } = new();
    public AddIngredientDialog()
    {
        this.InitializeComponent();
    }

    private void ingredientCategoryBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        ViewModel.Ingredient.Category = ingredientCategoryBox.SelectedItem as IngredientCategory;
    }
}

Category Model

public class IngredientCategory
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int? ParentId { get; set; }

    public IngredientCategory Parent { get; set; }

    public ICollection<Ingredient> Ingredients { get; set; }
    public Ingredient IngredientId { get; set; }
    public IngredientCategory() {}

    public IngredientCategory(int id, string name, int parentId)
    {
        Id = id;
        Name = name;
        ParentId = parentId;
    }
}

Ingredient Model

[Index(nameof(Name), IsUnique = true)]
public partial class Ingredient: BaseModel
{
    public int Id { get; set; }

    [ObservableProperty]
    [NotifyDataErrorInfo]
    [Required(ErrorMessage = "Name is Required")]
    [MinLength(2, ErrorMessage = "Name should be longer than one character")]
    private string _name;

    [ObservableProperty]
    private string _description;

    [ObservableProperty]
    private int _categoryId;
    public IngredientCategory Category { get; set; }

    //public Ingredient(string name, IngredientCategory category)

    public Ingredient()
    {
        SetProperty(ref _name, _name, true, nameof(Name));
    }      
    /*
    ~Ingredient()
    {
        ErrorsChanged -= Errors_Changed;
        PropertyChanged -= Property_Changed;
    }
    */
    public Ingredient(string name, string description, IngredientCategory category)
    {
        if (category == null)
        {
            Debug.WriteLine("category was null for " + name);
        }
        else
        {
            Name = name;
            Description = description;
            CategoryId = category.Id;
            //Category = category;
        }
    }
}