.NET MVC3 Preferred Model Initializiation

Question

I have been working in MVC recently, and I am curious about what the best way to initialize my view models is. Should I be mapping it directly in the controller, or should I be initializing the properties in a constructor for the view model. Also, when having lists, is this better practice since you will not have to repopulate them when there is a validation error.

For example, if i had the following model:

public FooBarViewModel
{
    public int FooBarId { get; set; }
    public string SomeInitialProperty1 { get; set; }
    public string SomeInitialProperty2 { get; set; }
    public string SomeInitialProperty3 { get; set; }
    public string SomeInitialProperty4 { get; set; }
    public int FooId { get; set; }
    public int BarId { get; set; }
    public IEnumerable<Foo> Foos { get; set; }
    public IEnumerable<Bar> Bars { get; set; }
}

and then the controller:

public MyController : Controller
{
    [HttpGet]
    public ActionResult FooBar(int foobarId)
    {
        var foobar = _fooBarRepository.GetById(foobarId);
        var model = new FooBarViewModel
                        {
                            FooBarId = foobar.Id;
                            SomeInitialProperty1 = foobar.SomeInitialProperty1;
                            SomeInitialProperty2 = foobar.SomeInitialProperty2;
                            SomeInitialProperty3 = foobar.SomeInitialProperty3;
                            SomeInitialProperty4 = foobar.SomeInitialProperty4;
                            Foos = foobar.Foos.ToList();
                            Bars = foobar.Bars.ToList();
                        }

        return View(model);
    }

    [HttpPost]
    public ActionResult FooBar(FooBarViewModel model)
    {
        if (ModelState.IsValid)
        {
             //process model
             return RedirectToAction("Index");
        }

        var foobar = _fooBarRepository.GetById(model.FoobarId);
        model.Foos = foobar.GetFoos.ToList();
        model.Bars = foobar.GetBars.ToList();
        return View(model);
    }
}

or should I do it in my model:

public FooBarViewModel
{
    public int FooBarId { get; set; }
    public string SomeInitialProperty1 { get; set; }
    public string SomeInitialProperty2 { get; set; }
    public string SomeInitialProperty3 { get; set; }
    public string SomeInitialProperty4 { get; set; }
    public int FooId { get; set; }
    public int BarId { get; set; }

    public IEnumerable<Foo> Foos 
    { 
        get { return _foos; }
    }
    private IEnumerable<Foo> _foos;

    public IEnumerable<Bar> Bars
    { 
        get { return _bars; }
    }
    private IEnumerable<Bar> _bars;

    public MyViewModel(FooBar foobar)
    {
        FooBarId = foobar.Id;
        SomeInitialProperty1 = foobar.SomeInitialProperty1;
        SomeInitialProperty2 = foobar.SomeInitialProperty2;
        SomeInitialProperty3 = foobar.SomeInitialProperty3;
        SomeInitialProperty4 = foobar.SomeInitialProperty4;
        _foos = foobar.Foos.ToList();
        _bars = foobar.Bars.ToList();
    }
}

then my controller:

public MyController : Controller
{
    [HttpGet]
    public ActionResult FooBar(int foobarId)
    {
        var foobar = _fooBarRepository.GetById(foobarId);
        var model = new FooBarViewModel(foobar);

        return View(model);
    }

    [HttpPost]
    public ActionResult FooBar(FooBarViewModelmodel)
    {
        if (ModelState.IsValid)
        {
             //process model
             return RedirectToAction("Index");
        }

        return View(model);
    }
}

Which is the preferred convention in MVC and why is it the best practice? Also, reasons why to choose one over the other? Thanks in advance.

Answer 1

By default, I do not believe MVC will use the DependencyResolver to create the instance of your view model on postback. As such, it will only create a model with a parameterless constructor. This makes it less easy to initialize the object in the constructor.

You could create a custom model binder that created the objectt through DependencyResolver, but then you are deviating from normal practice.

I prefer to inialize my view models with AutoMapper.