DataSource="{Binding AllCustomers}"

public ObservableCollection<CustomerViewModel> AllCustomers { get; set; }

public AllCustomersViewModel(ICustomerRepository repo)
{
            if (repo == null)
                throw new ParameterException(typeof(ICustomerRepository).ToString());

            _repo = repo;
            
            // Liste AllCustomers neu zusamensetzen
            AllCustomers = new ObservableCollection<CustomerViewModel>(
                from c in _repo.GetAll() select new CustomerViewModel(c,_repo));

}

/// <summary>
        /// Gets the customer entity.
        /// </summary>
        /// <value>The customer entity.</value>
        public Customer CustomerEntity 
        {
            get { return _customerEntity; }
        }
        private Customer _customerEntity;
/// <summary>
        /// Gets the customer ID.
        /// </summary>
        /// <value>The customer ID.</value>
        public int CustomerID
        {
            get { return _customerEntity.CustomerID; }            
        }

        /// <summary>
        /// Gets or sets the first name.
        /// </summary>
        /// <value>The first name.</value>
        public string FirstName
        {
            get { return _customerEntity.FirstName; }
            set
            {
                if (_customerEntity.FirstName != value)
                {                   
                    _customerEntity.FirstName = value;
                    RaisePropertyChanged("FirstName");
                }
            }
        }

public CustomerViewModel(Customer cust, ICustomerRepository repo)
        {
            // Parameter einstellen
            _repo = repo;
            _customerEntity = cust;
}