viewModel vs model who has responsability to communicate with business layer?

Question

Hi,

New to wpf and MVVM .I am kind of confused what belongs to what.

Lets suppose we have a view with a btnSave.

When saving who's the responsability to call the Business Layer ?

My understanding is that Model is just holding properties and no methods ViewModel is actually implementing EG " DelegateCommand SaveCommand and therefore calling the business layer. However I have been told that is actually responsability of the Model to call the business layer.

example taken from josh smith on msdn

Extract from there

      public ICommand SaveCommand
        {
        get
        {
            if (_saveCommand == null)
            {
                _saveCommand = new RelayCommand(param => Save(),param => CanSave);
            }
            return _saveCommand;
        }
    }

    /// <summary>
    /// Saves the customer to the repository.  This method is invoked by the SaveCommand.
    /// </summary>
    private void Save()
    {
        if (!_customer.IsValid)
            throw new InvalidOperationException(Strings.CustomerViewModel_Exception_CannotSave);

        if (this.IsNewCustomer)
            _customerRepository.AddCustomer(_customer);

        base.OnPropertyChanged("DisplayName");
    }

Your views very much appreciated.

Answer 1

The model is generally considered part of, if not the entire, business layer. So, the ViewModel should call methods in the Model (business layer).

Answer 2

The view typically binds to properties in the ViewModel. The ViewModel works (does the CRUD) with the Business Layer. An excellent article can be found here - http://msdn.microsoft.com/en-us/magazine/dd419663.aspx