Add editing to MVVM in a hierarchical data structure

Question

This question is a continuation of this older one , and it is more a confirmation than an open question.

In my ViewModel instance is a particular instance of the model _modelInst.
ViewModel has exclusive access to model data during editing (therefore, models do not need to implement INotifyPropertyChanged).

Now there are three ways I came up with how to edit model data from a view:

• Getting / setting directly in the model
  instance for example for simple value fields
  return _modelInst.fieldname;
_modelInst.fieldname = value;
  This easy to use ...

• Creating an instance of ViewModel and working with the parent data structure,
  for example, for more complex types of objects, such as structs:

  • Create a new ViewModel for this type.
    ViewModel knows the parent and its field name.
  • maps this to ContentControl + DataTemplate
  • receiving / setting:
    through the methods of the parent with the fieldname parameter as a parameter,
    overwriting the entire source object, even if only one field is changed.

  This means that for each of these structures a new interface is created (with update procedures working on _modelInst) implemented by the parent.

• Creating ViewModel instances without directly knowing the structure of the parent data,
  for example for (lists) of classes inside parent classes

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Answer 1

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Answer 2

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        -->Order

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public class CustomerView: // () {

public CustomerView(Customer customer)
{
      this.FirstName = customer.FirstName
      //etc..

      //Only if you need it, that is if you have some display-specific
      //logic relating to country for a given view, you create
      //a CountryView class that inherits from Country and gets populated
      //by an instance of it as well
      this.CountryView = new CountryView(customer.Country)
}

public CountryView CountryView {get;set;} //sadly you cannot override Country but you may be able to shadow it.

public string DisplayColor
{
    if(base.FirstName == "Joe")
    {
        return "red";
    }
    return "";
}

}

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