Domain Objects Causing NHibernate Errors

Question

Hi All,

I have a domain object that has been auto generated for me by MyGeneration. This is generated using an NHbernate template. This is part of the object - I have removed most of it,

[Serializable]
public class Purchase : INotifyPropertyChanged
{
    protected int id;

    public event PropertyChangedEventHandler PropertyChanged;

    public virtual int Id
    {
        get { return id; }
        set {if (value != this.id){id= value;NotifyPropertyChanged("Id");}}
    }
}

When I try to save one of these objects into the database I get an exception

NHibernate.InvalidProxyTypeException: The following types may not be used as proxies: NHibernateDemo.DataLayer.Entities.Purchase: method add_PropertyChanged should be 'public/protected virtual'

Etc. So if I change this line

public event PropertyChangedEventHandler PropertyChanged;

To this ...

public virtual event PropertyChangedEventHandler PropertyChanged;

It works, but to me this doesn't seem like a great solution. NHibernate is treating that event property like it is a field it is going to persist into the database. Is there a way I can tell NHibernate to ignore it?

If I make it a 'virtual event' do you think WPF binding will still work with it?

Answer 1

The exception means that NHibernate can't create a dynamic proxy of the object because the event is not virtual. NH creates a proxy of your object to allow for lazy loading. Your solution is fine.

Answer 2

You must be explicitly mapping this property in your NHibernate mapping file. Take a look at the generated hbm.xml file and remove this property from the mapping file so NHibernate will ignore it.