Question

I already have succesfully used MVVM principles in former projects, but i’m stuck with something … very basic!

Using EF4.1 (code first approach) as my data storage access which works fine. Created the following class:

public class Photo
    {
        [Key]       
        public int PhotoId { get; set; }
        public string Year { get; set; }
        public byte[] Thumbnail { get; set; }
        public DateTime InsertTime { get; set; }     //insertion time
        public DateTime UpdateTime { get; set; }     //last modification time


        //navigational properties
        public virtual Image Image { get; set; }
        public virtual Monument Monument { get; set; }//a Photo belongs to a specific Monument
        public virtual MDPremisesSpace MDPremisesSpace { get; set; } //a Photo was shot at specific premises space
        public virtual MDRestauration MDRestauration { get; set; }//a Photo has a restauration
        public virtual MDMaintenance MDMaintenance { get; set; }//a Photo has a maintenance
        public virtual MDType MDType{ get; set; }//a Photo has a type
        public virtual User InsertUser { get; set; }    //the user who inserted this reocord
        public virtual User UpdateUser { get; set; }   //the user who lastly modified this reocord

        //constructor
        public Photo()
        {            
        }
    }

Created a Viemodel based on that class (i ‘m using a Viewmodel based on generics, to resuse it whereever i can – with success), which implements INotifyPropertyChanged.In this viewmodel there is also a Property called Monuments which is defined this way (works fine):

private ObservableCollection<Model.Monument> monuments = new ObservableCollection<Model.Monument>();
public ObservableCollection<Model.Monument> Monuments
{
            get { return monuments; }
            private set { monuments = value; }

}

Created a view in which i used a combobox like this:

<ComboBox Name="cmbMonument" Grid.Row="1" Grid.Column="1" Width="200" HorizontalAlignment="Left"
                      ItemsSource="{Binding  Path=Monuments }"  
                      SelectedItem="{Binding Path=SelectedRecord.Monument,Mode=TwoWay,  UpdateSourceTrigger=PropertyChanged}"                       
                      DisplayMemberPath="Name"
                      />

The values are showing up correclty (and they can also be saved correctly).

BUT:

Is there anyone who can explain why changing the selected item in the combobox, it DOES NOT raise a property change notification??

If i would change the Year property the notification would get raised!!

(i’m suspecting the fact that the Monument property in the Photo class above is a navigational property…but even if it is like that, shouldn’t it raise a notification?)

Any hints are mostly welcome!!

Answer 1

Well it turns out that my suspicions where correct!

The correct way to declare this kind of code first class in EF4.1 is the following:

public class Photo
    {
        [Key]
        public int PhotoId { get; set; }
        public int? MonumentId { get; set; }
        public int? MDPremisesSpaceId { get; set; }
        public int? MDRestaurationId { get; set; }
        public int? MDMaintenanceId { get; set; }
        public int? MDTypeId { get; set; }
        public string Year { get; set; }
        public byte[] Thumbnail { get; set; }
        public int? InsertUserId { get; set; }        //the Id of user who inserted this record
        public DateTime InsertTime { get; set; }     //insertion time
        public int? UpdateUserId { get; set; }        //the Id of last user who modified this record
        public DateTime UpdateTime { get; set; }     //last modification time



        //navigational properties
        public virtual Image Image { get; set; }
        [ForeignKey("MonumentId")]
        public virtual Monument Monument { get; set; }//a Photo belongs to a specific Monument
        [ForeignKey("MDPremisesSpaceId")]
        public virtual MDPremisesSpace MDPremisesSpace { get; set; } //a Photo was shot at specific premises space
        [ForeignKey("MDRestaurationId")]
        public virtual MDRestauration MDRestauration { get; set; }//a Photo has a restauration
        [ForeignKey("MDMaintenanceId")]
        public virtual MDMaintenance MDMaintenance { get; set; }//a Photo has a maintenance
        [ForeignKey("MDTypeId")]
        public virtual MDType MDType { get; set; }//a Photo has a type
        [ForeignKey("InsertUserId")]
        public virtual User InsertUser { get; set; }    //the user who inserted this reocord
        [ForeignKey("UpdateUserId")]
        public virtual User UpdateUser { get; set; }   //the user who lastly modified this reocord

        //constructor
        public Photo()
        {
        }
    }

Notice that every Foreign Key association has ALSO its property in the class. Now the property change notification takes place!