how to scope C# view models

Question

I have a view that shows list of people. For said view I created a PersonListViewModel

class PersonListViewModel { 
    public IEnumerable<Person> People {get;set;}
    public int TotalPersonCount {get;set;}
    public int PeoplePerPage {get;set;}
    public string OrganizationName {get;set;}
}

My question is about Person class. Where should Person class be defined? And what should I call it?

This problem is an instance of more general problem of mapping types between bounded contexts or layers. I understand that I can use AutoMapper and such to do some of this work, but AutoMapper only alleviates the problem but does not solve it.

Here some options that I have considered along with pros and cons:

Put both PersonListViewModel and Person classes in the same namespace, e.g. Whatever.Organization.ViewModels.

Pro: Person class name shows what it is - a person, and context this class is bound to specified by namespace. Con: In a presenter where I build this Person instance will (most likely) collide with Person class from business domain space, so I will have to prefix one of them. Con: will have to add a namespace to contain view models (not necessarily a problem, since you might, and I do, already have a namespace for view models).

Nest Person inside PersonListViewModel class. Pro: Can have multiple Person classes for different view models. Pro: Person is naturally scoped to a view model it belongs to. Con: Can not reuse Person between views and view models. Inb4: I do believe that ViewModels shall not be reused, I do believe it is to reuse a non-viewmodel object definition in presentation layer when appropriate. This approach does not allow for such reuse, and in 5% of cases where it is necessary - I don't want to create a different pattern.

Postfix every presentation layer object with *ViewModel Pro: solves the problem of reuse and name collisions. Con: makes no sense since Person is only a view model when it contains data for a view, which might or might not be the case -- for example if person instance is given to a [sub]view - then, technically, it will be a view model, but if it is used as a property on PersonListViewModel then Person is not a view model (no more than int of TotalPersonCount is a view model, which it is not).

So far I don't have a solution that would make me happy. But solution #1 seems to be most correct (theoretically speaking), still I am hopeful a better solution will be suggested.

Answer 1

I would go with option 3. Why would a Person ever be passed to a view if it doesn't contain data for the view? ViewModels in general should only contain the data required by the view. There's nothing wrong with creating a PersonViewModel to pass data for a Person across that is to be consumed by the view. If the view doesn't require it, don't pass it across.

The fact that you are creating a PersonListViewModel implies that you are doing something presentational with a list of people in your view. It makes perfect sense to therefore create a PersonViewModel for holding the display data that you will be displaying in your view for each person held within your list.