After my last post about MEF + Factories, I was chatting with Glenn Block (PM for MEF) about my approach. One of the first things he mentioned is why I hadn't used an ExportProvider. As you know, ExportProvider's are new in the latest drop, and provide an interception point for resolving an import to an export.

Taking a look back at the documentation on ComposablePart, I can see why Glenn mentioned this. In it, it states that a ComposoblePart must adhere to to Import/Export contracts. If you've looked at the prior example, you'll see that I'm explicitly violating that rule as I'm finding interfaces based on a base interface, not by Export! At this point, my mind started churning - mainly because there's not a lot of examples or descriptions of what an ExportProvider actually is - but because I wanted to do things "correctly" according to the framework provided. (As an aside, Glenn stated that a "What is an Export Provider" post or documentation is coming, maybe this'll boost that necessity!) What I ultimately came up with was a much cleaner solution than using a FactoryPartCatalog.

Introducing FactoryExportProvider:

   1:  public class FactoryExportProvider<T> : ExportProvider {

   2:     public FactoryExportProvider(Func<Type, T> resolutionMethod) { }

   3:     public FactoryExportProvider(Assembly assembly, Func<Type, T> resolutionMethod) { }

   4:     public FactoryExportProvider(IEnumerable<Type> types, Func<Type, T> resolutionMethod { }

   5:  }

What you'll see is again, it's very straight forward and provides a clean implementation in usage, just as the part catalog example did. Each constructor does just as it had done in the part catalog, so I'll not explain that again. One thing that I discussed with Glenn about was, is it appropriate to look for certain types within an Export Provider? His response was "absolutely you can do that". good, I think I've found the correct implementation, both from less code/object graph standpoint, but also from an intention standpoint.

Internally, the code is very simplistic. Since I'm finding these interfaces on-the-fly, and need more information than just the contract name, I needed to use a FactoryExportDefinition to store this information. I've you've looked at the prior example, you'll see this came back out of necessity.

   1:  public class FactoryExportDefinition<T> : ExportDefinition {

   2:     public FactoryExportDefinition(string contractName, Type type, Func<Type, T> resolutionMethod) { }

   3:   

   4:     public override string ContractName { get { ... } }

   5:     public Type ServiceType { get; private set; }

   6:     public Func<Type, T> ResolutionMethod { get; private set; }

   7:  }

When finding all of the interfaces that implement the base interface specified in the FactoryExportProvider, I convert those into a list of FactoryExportDefinition objects. Reason being, is that the export provider compares an ImportDefinition to an ExportDefinition when finding all available exports. This comparison is done by implementing the GetExportsCore method. The idea of export providers, is that when resolving all dependencies, MEF will call into all of the registered ExportProviders to determine if they can supply the Export and will do a bunch of cardinality matching for you. Out of the box, MEF provides an export provider for it's registered part catalogs. Here's the FactoryExportProvider's implementation of GetExportsCore.

   1:  protected override IEnumerable<Export> GetExportsCore(ImportDefinition importDefinition) {

   2:     IList<Export> exports = new List<Export>();

   3:     var constraint = importDefinition.Constraint.Compile();

   4:     var foundExports = from d in definitions

   5:                        where constraint(d)

   6:                        select new Export(d, () => d.ResolutionMethod(d.ServiceType));

   7:   

   8:     if (importDefinition.Cardinality == ImportCardinality.ZeroOrMore)

   9:        exports = foundExports.ToList();

  10:     else if (foundExports.Count() == 1)

  11:        exports.Add(foundExports.First());

  12:   

  13:     return exports;

  14:  }

It's that simple. The Export's that are returned will have the resolution method called when the actual object is needed. When it comes down to including this within your application, it's just as easy as it was for the part catalog, you just register things a bit differently.

   1:  public interface IService { }

   2:  public interface IUserService : IService { }

   3:   

   4:  [Export]

   5:  public class UserController {

   6:     [ImportingConstructor]

   7:     public UserController(IUserService userService) { }

   8:  }

   9:   

  10:  // in your application

  11:  private void Compose() {

  12:     var catalog = new AttributedAssemblyPartCatalog(Assembly.GetExecutingAssembly());

  13:     var factoryProvider = new FactoryExportProvider<IService>(GetService);

  14:     var container = new CompositionContainer(catalog, factoryProvider);

  15:     container.AddPart(this);

  16:     container.Compose();

  17:  }

  18:   

  19:  public IService GetService(Type type) { return ... }

And that's it. Ultimately, this leads to a cleaner implementation that uses less types that you have to manage, and, adheres to the correct intentions of the framework. Much thanks to Glenn who I chatted with for several hours last night! You can get the downloadable source here. Enjoy!

Lately I've been really digging into MEF and have been looking at it's pros & cons, ease of use, extensibility, and the simple DI container that it can provide. I'm not going to give an overview of MEF, as others have done so already. What I am here to show off is a concept that may prove useful for some applications. Many of us use a DI container in very simplistic ways, as well as registering injection strategies during type resolution. If you have no needs of this latter, MEF is very simple and easily fits into your current architecture by not having to change anything but decorating things. For example:

   1:  public interface IUserService { }

   2:   

   3:  [Export(typeof(IUserService))]

   4:  [CompositionOptions(CreationPolicy = CreationPolicy.Factory)]

   5:  public class UserService : IUserService { }

   6:   

   7:  [Export]

   8:  public class UserController {

   9:     [ImportingConstructor]

  10:     public UserController(IUserService userService) { }

  11:  }

At MEF's simplistic nature, you see that during construction, our exported services are being imported for us, but only because we don't care about it's construction and assume that generic construction will work. So when we call resolve UserController using MEF, it'll create and inject a new instance of UserService for us.

Now, say we have a need where the construction of IUserService needs to go through a factory. For instance, maybe IUserService is a WCF endpoint, and you have custom logic built into properly constructing the proxy endpoint. Well, MEF can solve this issue for you by exporting methods, but what you have to do is ultimately change your code and have 2 constructors.

   1:  public interface IUserService { }

   2:   

   3:  // in your application

   4:  [Export(typeof(IUserService))]

   5:  public IUserService ConstructUserService() { return ... }

   6:   

   7:  [Export]

   8:  public class UserController {

   9:     [ImportingConstructor]

  10:     public UserController([Import(typeof(IUserService))] Func<IUserService> serviceMethod)

  11:         : this(serviceMethod())

  12:     { }

  13:   

  14:     public UserController(IUserService userService) { }

  15:  }

As you can see, it's not that nice. We need both constructors because one is used in production and one is used for testability. It ultimately leads to a lot of confusion as to why we need it. So, with that in mind, I set out to determine how this pattern could be achieved using MEF, but also provide a seamless transition from a DI world to MEF. Enter, FactoryPartCatalog:

   1:  public class FactoryPartCatalog<T> : ComposablePartCatalog {

   2:     public FactoryPartCatalog(Func<Type, T> resolutionMethod) { }

   3:     public FactoryPartCatalog(Assembly assembly, Func<Type, T> resolutionMethod) { }

   4:     public FactoryPartCatalog(IEnumerable<Type> types, Func<Type, T> resolutionMethod) { }

   5:   

   6:     public override IQueryable<ComposableDefinition> Parts { get { return ... } }

   7:  }

When we use this in our application, it brings back the simplicity of MEF. What it's doing during construction is looking through the assembly (first two constructors) to find all interfaces that implement type T. The interfaces that it finds will be created into ComposablePart's for MEF's container to utilize. Ultimately, when GetExportedObject<T> is called, it'll execute the resolution method you specified passing in the Type that was requested.

As you can see below, we're using a AggregatingComposablePartCatalog adding our new FactoryPartCatalog and AttributedAssemblyPartCatalog. We've told FactoryPartCatalog to look through the current assembly for all interfaces that derive from IService. Upon construction injection by MEF, it'll find that it's requesting an export of IUserService, find it in the FactoryPartCatalog, and call GetService(Type) to get it's instance.

   1:  public interface IService { }

   2:  public interface IUserService : IService { }

   3:   

   4:  [Export]

   5:  public class UserController {

   6:     [ImportingConstructor]

   7:     public UserController(IUserService userService) { }

   8:  }

   9:   

  10:  // in your application

  11:  private void Compose() {

  12:     var catalog = AggregatingComposablePartCatalog();

  13:     catalog.Catalogs.Add(new AttributedAssemblyPartCatalog(Assembly.GetExecutingAssembly()));

  14:     catalog.Catalogs.Add(new FactoryPartCatalog<IService>(GetService);

  15:     var container = new CompositionContainer(catalog);

  16:     container.AddPart(this);

  17:     container.Compose();

  18:  }

  19:   

  20:  public IService GetService(Type type) { return ... }

Now, there's a lot more code behind the scenes that is required to get a new Part Catalog up and running, but I'll leave that for you to check out in the downloadable source. As this is purely a proof of concept, I'm sure there's more simplifications or additions that can be added, but for getting this running out of the box in this manner, it works great!

Thanks to Brad, he identified a few areas that made things MUCH simpler from my prior implementation. Notably, while you still have your ViewEngine specify "here's your view's path" there's no longer a need for having a new helper, derived classes, etc. This implementation goes back to the simplified HtmlHelper extension in which you can use in any ViewEngine regardless. It also allows you to "replace" the implementation by just changing the namespace, just as you can do with Html and Ajax.

Simplified View Engine

As previously stated, you still need a new view engine and view, because this is the only point in which you can truly grab which view is being rendered. What's nice now, is that it has been simplified down to using the base implementation and only setting a ViewData field in which the Resource extension method picks up and uses.

   1:  public class LocalizationWebFormViewEngine : WebFormViewEngine

   2:  {

   3:      protected override IView CreateView(ControllerContext controllerContext, 

   4:                                                  string viewPath, string masterPath)

   5:      {

   6:          return new LocalizationWebFormView(viewPath, masterPath);

   7:      }

   8:   

   9:      protected override IView CreatePartialView(ControllerContext controllerContext, 

  10:                                                                            string partialPath)

  11:      {

  12:          return new LocalizationWebFormView(partialPath, null);

  13:      }

  14:  }

  15:   

  16:  public class LocalizationWebFormView : WebFormView

  17:  {

  18:      internal const string ViewPathKey = "__ViewPath__";

  19:   

  20:      public LocalizationWebFormView(string viewPath) : base(viewPath)

  21:      {

  22:      }

  23:   

  24:      public LocalizationWebFormView(string viewPath, string masterPath) 

  25:                : base(viewPath, masterPath)

  26:      {

  27:      }

  28:   

  29:      public override void Render(ViewContext viewContext, TextWriter writer)

  30:      {

  31:          // there seems to be a bug with RenderPartial tainting the page's view data

  32:          // so we should capture the current view path, and revert back after rendering

  33:          string originalViewPath = (string) viewContext.ViewData[ViewPathKey];

  34:          

  35:          viewContext.ViewData[ViewPathKey] = ViewPath;

  36:          base.Render(viewContext, writer);

  37:          

  38:          viewContext.ViewData[ViewPathKey] = originalViewPath;

  39:      }

  40:  }

As you can see, it's much simpler now. Also, it seems as if there's a bug with the current Beta bits when you have a RenderPartial on your page, there's no isolation and the view's path is not correct later. Simple fix by simply grabbing the original view path, setting it to the new path, rendering, and then reverting back.

Getting back to Extension Methods

And now that we have our path again in our ViewData, we can revert back to using extension methods to extract the path when doing both Global and Local resources. As you can see below, should you be using any other ViewEngine it will always work for Global resources.

   1:  public static class ResourceExtensions

   2:  {

   3:      public static string Resource(this Controller controller, string expression, 

   4:                                                    params object[] args)

   5:      {

   6:          ResourceExpressionFields fields = GetResourceFields(expression, "~/");

   7:          return GetGlobalResource(fields, args);

   8:      }

   9:   

  10:      public static string Resource(this HtmlHelper htmlHelper, 

  11:                                                    string expression, params object[] args)

  12:      {

  13:          string path = (string)htmlHelper.ViewData[LocalizationWebFormView.ViewPathKey];

  14:          if (string.IsNullOrEmpty(path))

  15:              path = "~/";

  16:   

  17:          ResourceExpressionFields fields = GetResourceFields(expression, path);

  18:          if (!string.IsNullOrEmpty(fields.ClassKey))

  19:              return GetGlobalResource(fields, args);

  20:   

  21:          return GetLocalResource(path, fields, args);

  22:      }

  23:   

  24:      static string GetLocalResource(string path, ResourceExpressionFields fields, 

  25:                                                       object[] args)

  26:      {

  27:          return string.Format((string)HttpContext.GetLocalResourceObject(path, 

  28:                                 fields.ResourceKey, CultureInfo.CurrentUICulture), args);

  29:      }

  30:   

  31:      static string GetGlobalResource(ResourceExpressionFields fields, object[] args)

  32:      {

  33:          return string.Format((string)HttpContext.GetGlobalResourceObject(

  34:               fields.ClassKey, fields.ResourceKey, CultureInfo.CurrentUICulture), args);

  35:      }

  36:   

  37:      static ResourceExpressionFields GetResourceFields(string expression, 

  38:                                                                string virtualPath)

  39:      {

  40:          var context = new ExpressionBuilderContext(virtualPath);

  41:          var builder = new ResourceExpressionBuilder();

  42:          return (ResourceExpressionFields)builder.ParseExpression(

  43:                                            expression, typeof(string), context);

  44:      }

  45:  }

Again, thanks to Brad, this implementation seems "less dirty". You can download the source for this here.

Update: Please see this newer post. It simplifies this solution drastically, and I don't recommend this version anymore!

I've previously blogged about how to add localization support within ASP.NET MVC before, but that codebase was based on Preview 3, and now that the beta is out there, the code just doesn't work anymore. Period. The concepts I had originally had put out there really don't fly well in the Beta world, or, within the "real" world in which people are using more than just the WebFormViewEngine for their rendering. So, why is there this big disconnect now? Well. it's not so much that global resources fail to work, it's more local resources don't really apply "generally" anymore.

While looking into a solution, and bouncing ideas off of Phil & Brad, I came to the realization that, just like in the Matrix, "There is no spoon" or rather, replace "spoon" with "view location" and you have your reasoning. Now, before you start ranting, let me explain. Yes, there are physical locations at which your views are located, but what if you're ViewEngine was pulling the view's from a database? No guarantee that a "general" solution could achieve local resource support based on a HtmlHelper extensino. However, if you left the local resource delegation up to a ViewEngine, you can now have a concept of a location in relevance to it. (And yes, the point may be moot if you use a different Resource Provider than the asp.net built-in one)

So where does that leave us? Well, we need a general way to access both global and local resources within a View, and global resources within a Controller. Ultimately, the code used to get the resources hasn't changed from my original implementation, however, because we no longer have that concept of a view location, the new implementation delegates this decision correctly to the view engine. Also, before I show the proof of concept, I want to warn you that the guts for my view rendering logic is nearly a copy from what is in the WebFormView source.

So here's the overall design is as follows:

1. Any view engine / views can out-of-the-box use "global resources"
2. A view engine can decide if it's views can participate in "local resources" by supplying it's own implementation.
3. A controller can request "global resources" for messages it's setting within ViewData.

Now, because I wanted to provide a default implementation for the WebFormViewEngine, the implementation isn't nearly as clean as one would like, but it does work great, and falls back to using non-derived ViewPage's and ViewUserControl's when necessary.

View Implementation

We start by deriving ViewPage and ViewUserControl to support localization. These new implementations will add a ResourceHelper, just like Ajax / Html / Url, so that within your view, you can directly access a resource.

   1:  public class LocalizedViewPage : ViewPage, ILocalizedView

   2:  {

   3:      public ResourceHelper Resource { get; set; }

   4:  }

   5:   

   6:  public class LocalizedViewPage<TModel> : ViewPage<TModel>, ILocalizedView

   7:      where TModel : class

   8:  {

   9:      public ResourceHelper Resource { get; set; }

  10:  }

  11:   

  12:  public class LocalizedViewUserControl : ViewUserControl, ILocalizedView

  13:  {

  14:      public ResourceHelper Resource { get; set; }

  15:  }

  16:   

  17:  public class LocalizedViewUserControl<TModel> : ViewUserControl<TModel>, ILocalizedView

  18:      where TModel : class

  19:  {

  20:      public ResourceHelper Resource { get; set; }

  21:  }

The interface ILocalizedView is simply an abstraction I put out so I could determine what type of View I was working with in the View Engine.

Resource Helper Implementation

The resource helper implementation is very straight forward. As previously stated, ResourceHelper is the base that adds support for global resources. The WebFormResourceHelper is what the new web form view engine implementation uses to add support for both global and local resources. As you'll see, WebFormResourceHelper is initialized with the virtual path of the currently rendering view so that it can correctly find the local resource.

   1:  public static class ResourceExtensions

   2:  {

   3:      public static string Resource(this Controller controller, 

   4:                                         string expression, params object[] args)

   5:      {

   6:          ResourceExpressionFields fields = GetResourceFields(expression, "~/");

   7:          return GetGlobalResource(fields, args);

   8:      }

   9:   

  10:      internal static string GetGlobalResource(ResourceExpressionFields fields, object[] args)

  11:      {

  12:          return string.Format((string)HttpContext.GetGlobalResourceObject(

  13:                                                      fields.ClassKey, fields.ResourceKey, 

  14:                                                      CultureInfo.CurrentUICulture), args);

  15:      }

  16:   

  17:   

  18:      internal static ResourceExpressionFields GetResourceFields(

  19:                                    string expression, string virtualPath)

  20:      {

  21:          var context = new ExpressionBuilderContext(virtualPath);

  22:          var builder = new ResourceExpressionBuilder();

  23:          return (ResourceExpressionFields)builder.ParseExpression(

  24:                                    expression, typeof(string), context);

  25:      }

  26:  }

  27:   

  28:  public class ResourceHelper

  29:  {

  30:      public virtual string GetString(string expression, params object[] args)

  31:      {

  32:          ResourceExpressionFields fields = GetResourceFields(expression, "~/");

  33:          if (string.IsNullOrEmpty(fields.ClassKey))

  34:              throw new InvalidOperationException(

  35:                       "The resource helper does not support local resources.");

  36:   

  37:          return GetGlobalResource(fields, args);

  38:      }

  39:   

  40:      protected string GetGlobalResource(ResourceExpressionFields fields, object[] args)

  41:      {

  42:          return ResourceExtensions.GetGlobalResource(fields, args);

  43:      }

  44:   

  45:      protected ResourceExpressionFields GetResourceFields(string expression, string virtualPath)

  46:      {

  47:          return ResourceExtensions.GetResourceFields(expression, virtualPath);

  48:      }

  49:  }

  50:   

  51:  public class WebFormResourceHelper : ResourceHelper

  52:  {

  53:      public WebFormResourceHelper(string virtualPath)

  54:      {

  55:          VirtualPath = virtualPath;

  56:      }

  57:   

  58:      public string VirtualPath { get; private set; }

  59:   

  60:      public override string GetString(string expression, params object[] args)

  61:      {

  62:          ResourceExpressionFields fields = GetResourceFields(expression, VirtualPath);

  63:          if (!string.IsNullOrEmpty(fields.ClassKey))

  64:              return GetGlobalResource(fields, args);

  65:   

  66:          return string.Format((string) HttpContext.GetLocalResourceObject(

  67:                                                             VirtualPath, fields.ResourceKey, 

  68:                                                             CultureInfo.CurrentUICulture), args);

  69:      }

  70:  }

You'll also notice that I've included a controller extension method for extracting global resources. This hasn't changed from the original implementation, but it's straight forward to use.

View Engine Implementation

This is where the rubber meets the road. Since we're now delegating that a ViewEngine can choose to support local resources, the derived view engine implementation is where it supplies it's own ResourceHelper, if it so chooses. In my example, I derive from the WebFormViewEngine and WebFormView, and provide this implementation to supply the WebFormResourceHelper to my localized views. For brevity, and the fact that I didn't write the code for rendering, I'll leave it up to you to see the full implementation for the LocalizedWebFormView in the download. However, the critical portion that you'll see is the following:

   1:  var localizedPage = page as ILocalizedView;

   2:  if (localizedPage != null)

   3:      localizedPage.Resource = new WebFormResourceHelper(ViewPath);

   4:  page.RenderView(context);

And that's it. In your view, you can now derive from LocalizedViewPage and get access to your global and local resources by doing

   1:  // global resource

   2:  <%= Resource.GetString("MvcExample, Welcome") %>

   3:   

   4:  // local resource

   5:  <%= Resource.GetString("Welcome") %>

How does this fit with other View Engines?

View engines need to simply add a reference to the ResourceHelper so that their view's can gain access to it. Obviously, they'll also need to change their ViewEngine to set an appropriate ResourceHelper when instantiating the view, but those view engines can explicitly determine how they would like to treat resources (even completely ignoring Global & Local resources).

And that's it, our View Engine now is completely in control of where my resources come from. They can use the baked-in ASP.NET resource provider, their own logic, or whatever! Again, this implementation is no where near baked, and I strongly urge you to look at your solution to see how this would fit in, and (obviously) make the code "production worthy". I'm hoping that some of these concepts make it into future MVC releases. You can also download the source for these files here. Enjoy!

So I've been checking over the source code for the latest ASP.NET MVC P4 release out on CodePlex, and have found some very interesting things.

 1. There's a variant codebase that is very similar to my RedirectToAction via Lambda expressions contained within the Futures/MvcFutures/Internal directory, "ExpressionHelper.cs". With this futures drop, the call will return a RouteValueDictionary, in which you turn around and call RedirectToRoute. In my version, of RedirectToAction, this is all taken care of for you, as well as it supports not having to explicitly give the type of your controller. Either way, here's the example on how to use this if you prefer:

   1:  using Microsoft.Web.Mvc.Internal;

   2:  using System.Web.Routing;

   3:   

   4:  public class HomeController : Controller

   5:  {

   6:     public ActionResult Index()

   7:     {

   8:        return View();

   9:     }

  10:   

  11:     public ActionResult DoRedirect()

  12:     {

  13:        RouteValueDictionary values = 

  14:           ExpressionHelper.GetRouteValuesFromExpression<HomeController>(c => c.Index());

  15:        return RedirectToRoute(values);

  16:     }

  17:  }

2. The RedirectToAction bug I blogged about has been fixed.

3. They've introduced a helper extension method (MvcControlDataBinder.SourceToDictionary) to convert data sources to a dictionary of values. The supported data source types include

1. DataSet
2. DataTable
3. IDataReader
4. IList
5. Array
6. IQueryable
7. IEnumerable

Below is an example on how to use this method. While I would never use this to convert a List of models normally, I could see where if you simply need to get truncated key/value list of data with various other sources like IDataReader or IQueryable, this would be beneficial.

   1:  public ActionResult Products()

   2:  {

   3:      List<Product> products = new List<Product>()

   4:      {

   5:          new Product(1, "16 Speed", 499.99m),

   6:          new Product(2, "24 Speed", 699.99m)

   7:      };

   8:   

   9:      Dictionary<object, object> data = 

  10:          MvcControlDataBinder.SourceToDictionary(products, "Id", "Name");

  11:      ViewData["Data"] = data;

  12:   

  13:      return View();

  14:  }

4. The new Ajax support. I'm not going to detail this as Scott Hanselman's post covered a good example and ScottGu will eventually give Part 2 which will be very detailed.

5. As ScottGu already indicated, the Mvc Framework comes with a bunch of new Action Filters, including

1. AuthorizeAttribute - which uses the membership framework for user authentication and user & role based security.
2. HandleErrorAttribute - which will enable you to handle exceptions that occur by rendering a specific view when an error occurs. This is equitable to the catch-all error page.
3. OutputCacheAttribute - Yes, this is what it says it is. Think ASP.NET output caching, and thats what this is.

6. TempData is now "testing friendly"! Well, right out of the box now, that is. They've introduced a new interface ITempDataProvider (and subsequent SessionStateTempDataProvider) that will only be used only when Execute is called from the Controller. The reason TempData is now tester friendly, is that by default it uses TempDataDictionary as a backing field, and Execute will Load/Save from the TempDataProvider set to/from TempData.

Just ran across this excellent post by Jeremy Skinner. Just shows on how much power & flexibility the new routing framework gives you. This really is making me want to really focus on my slack project of using Routing instead of Url Rewriting at work.

For the life of me, I can't seem to come up with any new blogging topics. At this point, I've exhausted all that's in MVC Preview 3, and haven't been doing anything super fun or cool at work lately. Hmmm, toss some things out and maybe I'll come up with something. Anyone?

On the flip side, I've fallen in love with Twitter - allows me to output my thoughts immediately.

<rant>

Wow, I never thought I'd hate a product so badly just starting to use it. If you've not tried out the new Entity Framework, give it a shot - but be ready to get frustrated and fast. The mere fact that I have to do half of my editing in pure XML and the other half in the designer is absurd. Why doesn't the designer support creating a new entity from my pre-loaded entity set from the database, or the ability to add a new property to my entity! Having to hop over to XML view just to add a new property is painful. I'm also all for "iterations" of code, but why is it when it's generating the model during compile time does it only give me 1 error at a time. Gar! I can't stand this - back to LINQ to SQL.

</rant>

I'm putting out a plea for help. For some odd reason, we have a WCF service (running in IIS 6) that's using streaming and BasicHttpBinding that will return a 404 error message every time it's called from our client. Hitting the same URL on the box itself through IE renders the WSDL just fine. If you have seen this issue, please contact me. We've been struggling with this issue and have yet to find a resolution. BTW, it works great on another web server that is configured the same, and we've looked at all of the verbose logs WCF can give us. Ultimately, we're seeing the message being sent from the client, and a 404 in the IIS log, but nothing on the server logging. Thanks!

I took some time to look back at my MVC Post-Redirect-Get sample and see where it could be improved as well as update it to use the MVC Preview 3 bits. What I found, is again, the core concepts didn't change that much. However, there are some new enhancements that Preview 3 gave us that makes our life a little bit easier. I'll save the full implementation for you to download and checkout yourself, but I do want to highlight some of these enhancements that made the source easier to use.

1. NameValueCollectionExtensions.CopyTo - this made it very nice for me to take all of the posted form data and copy it into the TempData so that upon a redirect, I could extract it out and put it in ViewData.

   1:  if (!BaseValidator.Validate(HttpContext.Request, validators)) {

   2:     NameValueCollectionExtensions.CopyTo(Request.Form, TempData);

   3:     TempData["ErrorMessage"] = BuildErrorMessage(validators);

   4:     return RedirectToAction("Create");

   5:  }

2. I added an extension method for IDictionary to copy between a source and destination, primarily for copying my TempData to ViewData. This way there is no need to do a manual copy of TempData objects all over the place, and is more resilient to changes and additions within your views and controller actions. I'm hoping this makes it into the MVC stack at some point so we all don't have to write this code ourselves.

   1:  public static void CopyTo(this IDictionary<string, object> source, 

   2:                            IDictionary<string, object> destination)

   3:  {

   4:      foreach (KeyValuePair<string, object> pair in source)

   5:      {

   6:          if (!destination.ContainsKey(pair.Key))

   7:              destination.Add(pair.Key, pair.Value);

   8:      }

   9:  }

The above code allows us to simply call the following line of code

   1:  TempData.CopyTo(ViewData);

3. What you'll notice, is that now all of my data is within ViewData, I can start to utilize the built-in functionality added in Preview 3 where the form controls will attempt to extract an initial value from ViewData. This mechanism really brings back the concept of ViewState, except that there is really no overhead to do this! Here's how my form now looks

   1:  <%@ Import Namespace="PRG.Controllers" %>

   2:  <asp:Content ID="Content1" ContentPlaceHolderID="MainContent" runat="server">

   3:  <% using (Html.Form<ProductsController>(c => c.Submit())) { %>

   4:      <h3>Create a New Product</h3>

   5:      Name: <%= Html.TextBox("Name") %><br />

   6:      Price: <%= Html.TextBox("Price") %><br />

   7:      Quantity: <%= Html.TextBox("Quantity") %><br />

   8:      <% if (ViewData["ErrorMessage"] != null) { %>

   9:          <br /><span style="color:red"><%= ViewData["ErrorMessage"] %></span><br />

  10:      <% } %>

  11:      <br />

  12:      <%= Html.SubmitButton() %>

  13:  <% } %>

  14:  </asp:Content>

4. While this next item isn't specifically related to Preview 3, it is a change from my last sample. Previously, I was doing all of my manual validations inline on the server, and it wasn't pretty. As you've probably been reading, I've been making some improvements to the MVC Validation within MvcContrib, and I decided I'd bring in that codebase to this sample. However, to truly show the full PRG pattern, I needed my form to post and alert me that there are errors on the page rather than relying upon client side validation; so I'm simply using the validator objects & server validation. In the next coming weeks, I'll be making another update to MvcContrib to do model based validation. I'll leave this code for your viewing or other examples on my blog.

And that's the updated sample. You can downloaded the latest bits from here. Please let me know what you think and anything else you would do to change this. As each iteration of the MVC framework is released, the sample gets easier and easier! Hope you enjoy this.