title: Update Entity Framework property when different property in model is changed
body: <p>I have an Entity Framework model </p>
  
  <pre><code>public partial class Product
  {
      public Product()
      {
          this.Designs = new HashSet&lt;Design&gt;();
      }
  
      public int BookingProductId { get; set; }
      public System.Guid BookingId { get; set; }
      public decimal Price { get; set; }
  
      public virtual Booking Booking { get; set; }
      public virtual ICollection&lt;Design&gt; Designs { get; set; }
  }
  </code></pre>
  
  <p>...in which I would like to update the Price property in response to a new Design being added to the Product. I've tried to follow this example:</p>
  
  <p><a href="https://stackoverflow.com/questions/17073114/how-can-i-change-an-entity-framework-icollection-to-be-an-observablecollection">How can I change an Entity Framework ICollection to be an ObservableCollection?</a></p>
  
  <p>so my class reads as follows:</p>
  
  <pre><code>public partial class Product : INotifyPropertyChanged
  {
      public Product()
      {
          this.Designs = new ObservableCollection&lt;Design&gt;();
      }
  
      public int BookingProductId { get; set; }
      public System.Guid BookingId { get; set; }
      public decimal Price { get; set; }
  
      public virtual Booking Booking { get; set; }
      public virtual ObservableCollection&lt;Design&gt; Designs { get; set; }
  
      public event PropertyChangedEventHandler PropertyChanged;
      protected void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
      {
          var handler = PropertyChanged;
          if (handler != null)
          {
              handler(this, new PropertyChangedEventArgs(propertyName));
          }
      }
  }
  </code></pre>
  
  <p>but if I add a new Design to the Product as so </p>
  
  <pre><code>product.Designs.Add(new Design());
  </code></pre>
  
  <p>then the NotifyPropertyChanged method is never fired. Does anyone know why???</p>
  
  <p>Thanks in advance</p>