Merging and combining dynamic/expando objects in C#

I ran into a very interesting situation today where I needed to merge two dynamically created objects in a very similar way to the way that the jQuery Extend method works.

The scenario was that I was creating my own custom override for the MVC DropDownListFor helper and needed to be able to both accept html attributes and had a number of attributes that I wanted to preset.

So the basic method looked like this.

public static MvcHtmlString DropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<System.Func<TModel, TProperty>> expression, string ajaxDataSourceUrl, object htmlAttributes)
{
    dynamic attributes = Merge(new
    {
        @class = "AjaxDropDown",
        data_AjaxDataSourceUrl = ajaxDataSourceUrl,
    }, htmlAttributes);

    MvcHtmlString dropDownList = System.Web.Mvc.Html.SelectExtensions.DropDownListFor(htmlHelper, expression, new List<SelectListItem>(), attributes);
    return dropDownList;
}

The actual Merge method looks like this.

private static dynamic Merge(object item1, object item2)
{
    IDictionary<string, object> result = new ExpandoObject();

    foreach (var property in item1.GetType().GetProperties())
    {
        if (property.CanRead)
            result[property.Name] = property.GetValue(item1);
    }

    foreach (var property in item2.GetType().GetProperties())
    {
        if (property.CanRead)
            result[property.Name] = property.GetValue(item2);
    }

    return result;
}

Note however that the above implementation does not take into account the possibility that both dynamics may contain the same property and in the current implementation will override each other.

Microsoft MVC5 + ASP.NET Identity with Telerik OpenAccess Awesomeness

Microsoft’s new membership system ASP.NET Identity is (IMHO) absolutely fantastic! The system itself comes installed as the default provider in Visual Studio 2013 for ASP.NET templates and can be downloaded for use within Visual Studio 2012.

ASP.NET Identity is the next step in the evolution to what was previously known as the SimpleMembership and Membership providers. Previous versions have been extremely brittle; this new approach simplifies and segments the membership provider in such a way that it makes it incredibly easy to plug-in and remove the components as you require and more importantly simplifies development when implementing a separation of concerns in a Service Oriented Architecture. Anyone who has attempted to achieve this with WCF and the previous membership providers will know the difficulties and lack of clear process through which to accomplish this. Another major benefit is that the framework implements all the .NET Async goodness by default. While you could always create your own Async wrappers in the older providers it makes things easier to see this functionality implemented for you.

The problems with the original ASP.NET Membership provider were:

  1. Designed for SQL Server and you can’t change it. You can add profile information, but the additional data is packed into a different table, which makes it difficult to access by any means except through the Profile Provider API.

  2. The provider system enables you to change the backing data store, but the system is designed around assumptions appropriate for a relational database.

  3. Since the log-in/log-out functionality is based on Forms Authentication, the membership system can’t use OWIN.

As the Introduction to ASP.NET identity article goes on to say

Simple Membership did make it easier to customize user profile information, but it still shares the other problems with ASP.NET Membership, and it has some limitations such as:

  • It was hard to persist membership system data in a non-relational store.
  • You can’t use it with OWIN.
  • It doesn’t work well with existing ASP.NET Membership providers, and it’s not extensible.

So, how is ASP.NET Identity different? Well…..

1. Storage backend is completely separate

Complete and total separation of the storage mechanism used within the provider. For example implement your own storage back-end but use something other than the entity framework? Or you want to use some type of NoSQL implementation (such as Azure Tables) or even just an Xml file? Well all you need to do¹ is implement the IUser and the IUserStore interfaces, inject it into your UserManager and you’ve got your own custom storage provider.

Example.

protected void CreateUserManager()
{
    //Create a new user manager based on your User model, inject your UserStore and finally your ORM context
    UserManager<AspNetUser> Manager = new UserManager<AspNetUser>(new OpenAccessUserStore(new EntitiesModel()));

    //Now inject the validator
    Manager.UserValidator = new UserValidator<AspNetUser>(Manager)
    {
        AllowOnlyAlphanumericUserNames = false
    };

    //And set a property so you can use the UserManager when required
    this.UserManager = Manager;
}

//Public property to access your UserManager instance.
public UserManager<AspNetUser> UserManager { get; private set; }

Note that all you need to do to create a basic IUserStore and IUser is implement this.

public interface IUserStore<TUser> : System.IDisposable where TUser : Microsoft.AspNet.Identity.IUser
{
    System.Threading.Tasks.Task CreateAsync(TUser user);
    System.Threading.Tasks.Task UpdateAsync(TUser user);
    System.Threading.Tasks.Task DeleteAsync(TUser user);
    System.Threading.Tasks.Task<TUser> FindByIdAsync(string userId);
    System.Threading.Tasks.Task<TUser> FindByNameAsync(string userName);
}

AND THIS

public interface IUser
{
    string Id { get; }
    string UserName { get; set; }
}

2. General decoupling

Previously the provider implementation was extremely closely coupled between its various ‘bits’. The result would often cause confusion about which methods to invoke and under what circumstances (at least for me). Sometimes all you’d want to do is authenticate, sometimes you want to authenticate and sign in and sometimes you want to go straight to the database and just retrieve some bit of User info. Because of this change of implementation it’s been significantly easier to build a project using this provider and integrate it with WCF cleanly. In part this is because it’s now much easier to say, “Give me all claims for this user.” then “Authenticate the following claims.”. They are completely different subsystems and have no direct inter-dependencies.

3. Unit Testing

Clear interface based contracts between the various components of the framework make dependency injection and unit testing much simpler.

4. Claims based

While roles still exist within ASP.NET Identity the emphasis to a claims based authentication seams clear. Claims are useful because they abstract the individual elements of identity and access control into two parts. Unless you’ve got a reason not to, I suggest it makes sense to use claims rather than roles.


Finally I’ve gone ahead and built a generic Visual Studio project template extension which shows how to integrate MVC5 with ASP.NET Identity behind WCF webservices and utilizing Telerik OpenAccess ORM for the storage provider (Because OpenAccess kicks ass…) and deployed it to the Visual Studio Gallery for everyone to use or if you prefer just a straight download of the files.

The project itself demonstrates a number of things including:

  1. How to create a NetTCP WCF service without autogenerated proxy classes.
  2. How to use ASP.NET Identity in a WCF service
  3. How to use a different ORM as an alternative to the entity framework
  4. How to include System.ComponentModel.DataAnnotations in a portable class library for your Views.
    1. Which allows the ability to use them across your MVC, WCF, Windows Phone and Xamarin applications.

Hopefully someone else will find the template and source code useful!


  1. It’s not quite that simple (you might need to implement between 1 and like 10,000,000 interfaces), but almost!

Using WebMatrix, SimpleMembershipProvider in WCF service and the “This method cannot be called during the application’s pre-start initialization stage” error.

Having made the transition to using MVC architecture for all my new applications I recently came across a situation where I needed to use the WebMatrix membership provider within my WCF services. It wasn’t a trivial process so I thought I would document it here.

So how do you get access to the SimpleMembershipProvider in WCF?

First add the references to the WebMatrix dlls

references

Second add the Web.Config reference in system.web as such

<membership defaultProvider="SimpleMembershipProvider">
  <providers>
    <add
      name="SimpleMembershipProvider"
      type="WebMatrix.WebData.SimpleMembershipProvider, WebMatrix.WebData"
      connectionStringName="MyApplicationConnectionString"
      applicationName="MyApplicationName"
      enablePasswordRetrieval="false"
      enablePasswordReset="true"
      requiresQuestionAndAnswer="false"
      requiresUniqueEmail="true"
      passwordFormat="Hashed" />
  </providers>
</membership>

Making sure you select your defaultProvider as SimpleMembershipProvider.

Lastly make sure the required assemblies are referenced in the web.config system.web.compilation.assemblies section as such.

<compilation debug="true" targetFramework="4.5">
  <assemblies>
    <add assembly="WebMatrix.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
    <add assembly="WebMatrix.WebData, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
  </assemblies>
</compilation>

and at that point you should be able to do this.

SimpleMembershipProvider provider = (SimpleMembershipProvider)System.Web.Security.Membership.Provider;

and use the provider now as you as you normally would i.e. ValidateUser(), ChangePassword() etc…

However at this point I ran into an issue where the following error appeared. “Parser Error Message: This method cannot be called during the application’s pre-start initialization stage.”. The solution to this problem was the following StackOverflow post and adding the these into my appSettings.

<appSettings>
  <add key="autoFormsAuthentication" value="true"/>
</appSettings>

Which successfully fixed the problem and everything worked at that point.

Always use ChannelFactory when referencing WCF services (particularly for Azure)

Given the indeterminate nature of the IP addresses of Azure web roles (There are a number of exceptions to this but in general) you end up in a real pickle if you you use the Service Reference functionality built into Visual Studio that most of us regularly do.

(This thing)

Image

Truthfully, the way the proxy service references have always worked had its flaws despite its convenience.

The problem boils down to two things. First, if you’re correctly using WCF services you should be binding to DataContracts and Interfaces rather than any concrete implementations anyway. Secondly, you’re stuck with hard-coded values that live in your web.config, with what is inherently dynamic and often not known at compile time (ip addresses).

So how do you solve it?

Remarkably simply, it takes the form of the channel factory and provided you have both your datacontracts and your service interfaces referenced you can then do this.

Image

Download the example.

 

Calling WebAPI service from Windows Phone 8 using HttpClient

I had to solve what I figure must be a typical problem for a windows phone developer today, invoking a WebAPI service from the Mobile side. I found documentation on this process rather scarce, so here’s how you do it.

NuGet is your friend in this regard.

Step 1.

PM>  Install-Package Microsoft.AspNet.WebApi.Client -Pre

Step 2.
Confirm references

References

Step 3.

Now you can use  the HttpClient Async API to invoke your WebAPI service and return data. Here’s an example.

code

Which can then be used like this

StockService

To download the source click here.