Business Entity Loading Pattern

public class Relation<T>
{
  private T _value;

  private void FetchData()
  {
    if( LoadData != null ) {
      LoadDataEventArgs args = new LoadDataEventArgs(typeof(T), /* magic to get correct object */);
      LoadData(this, args);
      _value = (T)args.Value;
    }
  }

  public event EventHandler<LoadDataEventArgs> LoadData;

  public T Value {
    get {
      if( _value == default(T) )
        FetchData();
      return _value;
    }
    set { /* Do magic here. */ }
  }
}

[RelationCriteria("ID", EqualsMyProperty="AddressID")]
public Relation<Address> Address {
  get; set;
}