public class EntityService : IEntityService
{
    public EntityService()
    {
        _entities = new DatabaseDomainContext();
    }

    private DatabaseDomainContext _entities;
    public DatabaseDomainContext Entities
    {
        get { return _entities; }
        set { _entities = value; }
    }

    private EntityList<Objective> _objectives;
    public ObservableCollection<Objective> Objectives
    {
        get
        {
            if (_objectives == null)
            {
                var loadOp = _entities.Load(_entities.GetObjectivesQuery()/*, Callback, true*/);
                _objectives = new EntityList<Objective>(_entities.Objectives, loadOp.Entities);
            }

            return _objectives;
        }
    }
}