asp.net-mvc - 谁负责加载数据？

Question

在MVC模型中，加载 View 模型的职责在哪里？

Controller 应该加载数据吗？如果 View 模型本身加载数据ala: MyViewModel viewModel = MyViewModel.Create(someValue);服务层是否应该加载它: MyViewModel viewModel = MembershipService.Instance.Load(someValue);

Answer 1

请参阅这个真正干净技术的示例: http://www.lostechies.com/blogs/jimmy_bogard/archive/2009/06/29/how-we-do-mvc-view-models.aspx

或者，您也可以手动执行此操作:请参阅“ASP.NET MVC In Action”一书或 CodeCampServer示例来源。基本上你注入(inject) IViewModelMapper { public ViewModel Map(data); } 到 Controller 。巧妙的是，它使您的 IoC 自动将服务和存储库传递给您的 ViewModel 映射器。然而，这确实会使 Controller 因映射器接口(interface)而变得臃肿，因此像 Jimmy Bogard 的技术一样，即使没有 AutoMapper，但使用操作过滤器也比选择 IViewModelMapper 会更好。

如果你做不到这一点，那么我建议坚持使用 ViewModel 处理映射，如 Mathias 建议的那样。

更新:这是一个使用 CodeCampServer 方式进行类似自动映射器配置的示例。不确定它是否会按原样工作(或根本有用)，只是一个演示。

public abstract class ViewModelMapper<Source, ViewModel> where Source: class, ViewModel: IViewModel
{
  public abstract ViewModel Map(Source source);
}

public class ProductDetailsViewModel
{
  public ProductViewModel Product { get; set; }
  punlic IList<Language> AvailableProductLanguages { get; set; }
}

public class ProductDetailsViewMapper: ViewModelMapper<Product, ProductDetailsViewModel>
{
  private ILanguageRepository languages;
  public ProductDetailsViewMapper(ILanguageRepository languages)
  {
     this.languages = languages;
  }
  public override ProductDetailsViewModel Map(Product source)
  {
     var vm = new ProductDetailsViewModel();
     AutoMapper.Map<Product, ProductDetailsViewModel>(product, vm);
     vm.AvailableProductLanguages = languages.GetAppropriateFor(product);
  }
}

public class ViewModelMapperActionFilter: ActionFilter
{
  Type mapperType;
  public ViewModelMapperActionFilter()
  {
  }
  public ViewModelMapperActionFilter(Type mapperType)
  {
  }
  public void OnActionExecuted(ControllerContext context)
  {
    var model = context.Result.ViewData.Model;
    var mapperType = this.MapperType ?? this.GetMapperTypeFromContext(context);
    // this is where magic happens - IoC grabs all required dependencies
    var mapper = ServiceLocator.GetInstance(mapperType);
    var method = mapperType.GetMethod("Map");
    Check.Assert(method.GetArguments()[0].ArgumentType == model.GetType());
    context.Result.ViewData.Model = method.Invoke(mapper, new[]{model});
  }
}

public class ProductsController: Controller
{
  [ViewModelMapper(typeof(ProductDetailsViewMapper))]
  // alternatively [ViewModelMapper()] will auto-pick mapper name by controller/action
  public ActionResult Details(EntityViewModel<Product> product)
  {
    // EntityViewModel is a special type, see 
    // http://stackoverflow.com/questions/1453641/my-custom-asp-net-mvc-entity-binding-is-it-a-good-solution
    return View(product.Instance); 
  }
}

//Global.asax.cs:
IoC.Register(AllTypes.DerivedFrom(typeof(ViewModelMapper<>)));