View difference between Paste ID: Aj47DqyV and qzhkueKe

 //Item.cs
     public class Item
     {
         public Item()
         {
-            Composites = new HashSet<Item>();
+            Composites = new HashSet<ItemItem>();
-            Components = new HashSet<Item>();
+            Components = new HashSet<ItemItem>();
         }
-
+
         public int ItemId { get; set; }
 
         public string Name { get; set; }
 
         public int Cost { get; set; }
 
-        public virtual ICollection<Item> Composites { get; set; }
+        public virtual ICollection<ItemItem> Composites { get; set; }
 
-        public virtual ICollection<Item> Components { get; set; }
+        public virtual ICollection<ItemItem> Components { get; set; }
 
         public void AddComponent(MyContext context, Item item, [Range(1, Int32.MaxValue)] int quantity = 1)
         {
             var itemRelation = Components.FirstOrDefault(c => c.Composite == this);
             if (itemRelation == null)
             {
                 itemRelation = new ItemItem() { Composite = this, Component = item, Quantity = quantity };
                 this.Components.Add(itemRelation);
                 item.Composites.Add(itemRelation);
             }
             else
             {
-        protected override void OnModelCreating(DbModelBuilder modelBuilder)
+                itemRelation.Quantity += quantity;
             }
-            modelBuilder.Entity<Item>()
+
-                .HasMany(x => x.Composites)
+
-                .WithMany(x => x.Components);
+        public void AddComposite(MyContext context, Item item, [Range(1, Int32.MaxValue)] int quantity = 1)
         {
             var itemRelation = Composites.FirstOrDefault(c => c.Component == this);
             if (itemRelation == null)
             {
-    public partial class MainWindow : Window
+                itemRelation = new ItemItem() { Component = this, Composite = item, Quantity = quantity };
                 this.Composites.Add(itemRelation);
                 item.Components.Add(itemRelation);
             }
             else
             {
                 itemRelation.Quantity += quantity;
             }
         }
     }
 
 //ItemItem.cs
     public class ItemItem
     {
         public ItemItem()
         {
 
-                Item i3 = new Item() { Name = "System Unit", Cost = 250 };
+
 
         [Key]
         public int RelationId { get; set; }
 
         public int Quantity { get; set; }
 
-
+        public virtual Item Composite { get; set; }
-                i3.Components.Add(i1);
+
-                i3.Components.Add(i2);
+        public virtual Item Component { get; set; }
-                i1.Composites.Add(i3);
+
-                i2.Composites.Add(i3);
+
 //MyContext.cs
     public class MyContext : DbContext
     {
         public MyContext()
             :base("DbConnection")
         { }
 
         public DbSet<Item> Items { get; set; }
 
         public DbSet<ItemItem> ItemItems { get; set; }
     }
 
 //MainWindow.xaml.cs
 public partial class MainWindow : Window
     {
         public MainWindow()
         {
             InitializeComponent();
 
             AppDomain.CurrentDomain.SetData("DataDirectory", AppDomain.CurrentDomain.BaseDirectory);
         }
 
         private void Window_Loaded(object sender, RoutedEventArgs e)
         {
             Database.SetInitializer<MyContext>(new CreateDatabaseIfNotExists<MyContext>());
 
             using (MyContext context = new MyContext())
             {
 
                 Item i1 = new Item() { Name = "Motherboard", Cost = 500 };
                 Item i2 = new Item() { Name = "Network Adapter", Cost = 150 };
                 Item i3 = new Item() { Name = "System Unit", Cost = 0 };
 
                 context.Items.Add(i1);
                 context.Items.Add(i2);
                 context.Items.Add(i3);
 
                 context.SaveChanges();
 
                 i3.AddComponent(context, i1);
                 i3.AddComponent(context, i2);
 
                 context.SaveChanges();
             }
         }
     }