Update Entity Framework property when different property in model is changed

Question

I have an Entity Framework model

public partial class Product
{
    public Product()
    {
        this.Designs = new HashSet<Design>();
    }

    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<Design> Designs { get; set; }
}

...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:

How can I change an Entity Framework ICollection to be an ObservableCollection?

so my class reads as follows:

public partial class Product : INotifyPropertyChanged
{
    public Product()
    {
        this.Designs = new ObservableCollection<Design>();
    }

    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<Design> Designs { get; set; }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
    {
        var handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

but if I add a new Design to the Product as so

product.Designs.Add(new Design());

then the NotifyPropertyChanged method is never fired. Does anyone know why???

Thanks in advance

Based on some answers to other questions, I wonder if you should look at the `INotifyCollectionChanged` event. — Ann L., Nov 22 '13 at 11:49

score 4 · Answer 1 · answered Nov 22 '13 at 11:55

NotifyPropertyChanged never fires because adding another element to your Designs collection doesn't actually change any Product's properties. If you want to track changes within the collection itself, it should implement INotifyCollectionChanged interface. ObservableCollection already implements that, so you can simply handle CollectionChanged event.

score 3 · Accepted Answer · edited Jun 17 '15 at 09:51

3

NotfiyPropertyChanged will only called when you set the whole collection and not the included items.

This is a workaround for the problme:

public partial class Product : INotifyPropertyChanged
{
    public Product()
    {
        this.Designs = new ObservableCollection<Design>();
        this.Designs.CollectionChanged += ContentCollectionChanged;
    }

    public void ContentCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        // This will get called when the collection is changed
        // HERE YOU CAN ALSO FIRE THE PROPERTY CHANGED 
    }

    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<Design> Designs { get; set; }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
    {
        var handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

edited Jun 17 '15 at 09:51

Hossein Narimani Rad

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answered Nov 22 '13 at 12:05

Bassam Alugili

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That's great , thanks very much. I've noticed also now that the ContentCollectionChanged event is fired when I retrieve the product object from the database and .Include the designs, which makes sense but I wonder if there is any way to differentiate this from when I .Add(new Design()); ??? – ledragon Nov 22 '13 at 12:18
Normally you do not have to that, let say you are using MVVM pattern and you have bound your collection to a ListBox. The ListBox will fire this event for example SelectedItem(s)Changed etc. – Bassam Alugili Nov 22 '13 at 12:29
Not sure I understand that...Can I rephrase? I've retrieved a Product and associated Designs from the DB: var product = this.GetDbSet().Include(c => c.BookingDesigns).Single(c => c.BookingProductId == bookingProductId); At this point each time a Design is added to the product the ContentCollectionChanged is fired. Then I wish to add a new Design as so...product.Designs.Add(new Design()); and the ContentCollectionChanged is also fired. It is at this point I wish to perform an action on the Price property of Product rather than when I retrieve from DB. Does that make sense? – ledragon Nov 22 '13 at 12:38

Update Entity Framework property when different property in model is changed

2 Answers2