WPF MVVM View with lookup or join to other entities - wpf

Question

I am getting started with WPF and MVVM. I am just reading up on Code Project Article which is quite interesting and provides a good quick start. I am using Entity Framework and I am happy I have listed all of my entities in a ListView.
I am curious how you would correctly implement lookups - in the view model or create a new model. Take the simple case of a person. The data structure might be:
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
public DateTime DateOfBirth { get; set; }
public Toy FaveToy { get; set; }
}
public class Toy
{
public string Name { get; set; }
public string Model { get; set; }
public string Manufacturer { get; set; }
}
I want my list view to show the columns FirstName, LastName, DateOfBirth, Fave Toy, Manufacturer.
The Toy field will be a combined string with Name + " " + Model in.
So given some of the code in the example I've linked (I've knocked the Person class up for examples sake):
Base Class for the views
public abstract class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
My implementation for the Person view
public class PersonViewModel : ViewModelBase
{
private ObservableCollection<Person> _Person;
public PersonViewModel()
{
_Person = new ObservableCollection<Person>();
Entities context = new Entities();
foreach(var person in context.Person.ToList())
{
_Person.Add(person);
}
}
public ObservableCollection<Person> Person
{
get
{
return _Person;
}
set
{
_Person = value;
this.OnPropertyChanged("Person");
}
}
}

Answer 1

If I am understanding correct you want to access a Toy through the FaveToy property automatically.
Normally this would be done creating a relation between Person and Toy. Once you've done so your Person entity type would look like this:
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
public DateTime DateOfBirth { get; set; }
public virtual Toy FaveToy { get; set; }
}
Notice the "virtual" on FaveToy. This indicates a navigation property which would be accessible through person instance.FaveToy. This can be represented in XAML either through dot notation or using the path property on your binding. Here is a link that discusses navigation properties: http://msdn.microsoft.com/en-us/data/jj713564.aspx
If you want to represent the toy by a combination of name and model then a converter would do the trick on the binding. Here is a link that discusses converters http://msdn.microsoft.com/en-us/library/system.windows.data.ivalueconverter.aspx
Hope this helps...Jason
PS - Josh Smith is awesome in his discussion of WPF and MVVM http://joshsmithonwpf.wordpress.com/a-guided-tour-of-wpf/
If you're a VB guy Alessandro has trhe best discussion for VB that I've seen: http://community.visual-basic.it/Alessandroenglish/archive/2010/08/13/31861.aspx
PSS -- WPF and MVVM (or Windows 8 and XAML) are awesome. Definitely worth your time to pick up.