Skip to main content

Dependency Injection through XML configuration and XML transformation through SlowCheetah

Dependency Injection (DI) is a design pattern to change definition by substituting object without changing code for the application. The most popular DI type is to construct classes based on certain interface and pass actual object on constructor level.

What are we trying to do?
We will be looking into a way to achieve dependency injection through XML configuration based on build selection. The implemented classes derived through interface will get switched based on build selection.

Where to use it?
I really hate making dependencies with something specific which can be changed later on. In my case, Azure environment. I believe Azure is more like a platform where we can host the application rather then integrating the application with Azure. What if client decided to switch to other hosting environment, in that case we got to change every piece of code wherever Azure SDKs are referred.

The above one is merely an example. We can use this approach on many other item as well.

What tools are used?
Ninject(http://www.nuget.org/packages/Ninject): This is going to used for dependency injection.
Ninjeect.Extensions.Xml (http://www.nuget.org/packages/Ninject.Extensions.Xml): This will be used to construct Ninject kernel through XML file.
SlowCheetah (http://visualstudiogallery.msdn.microsoft.com/69023d00-a4f9-4a34-a6cd-7e854ba318b5): An extension of Visual Studio to transform config or XML files.

Processes to do DI through SlowCheetah
I am expecting that you have installed the above tools at this point.

Step 1 - Creating main XML:
Let's start by creating NinjectInjection.xml file with required injections.

 <?xml version="1.0" encoding="utf-8" ?>  
 <module name="MyProjectInjection">  
  <bind  
   service="MyProject.Interface.Cache.ICacheWrapper, MyProject.Interface"  
   to="MyProject.Core.Caching.AppMemoryCache, MyProject.Core" />  
  <bind  
   service="MyProject.Interface.Cache.IAppCache, MyProject.Interface"  
   to="MyProject.Core.Caching.AppCache, MyProject.Core" />  
  <bind  
   service="MyProject.Interface.Uploader.IFileUpload, MyProject.Interface"  
   to="MyProject.Core.Uploader.Local.LocalFileUpload, MyProject.Core" />  
 </module>  

You can see, I have configured injections for Caching and File uploading mechanism which will support local file system and Memory Caching on IIS. Based on selection of build we will switch definition to Azure Caching and Azure BLOB storage or normal IIS approach.

Step 2 - Creating dependent XML files:
Right click on created  XML file and select Add Transform which will generate up XML files based on build profiles.





Generated XML files. In this case, I am having NinjectInjection.AzureLocalTest.xml as extra item as per my build configuration profile.





Step 3 - Transforming XML files based on our need:
The idea is to find particular element (bind element) in desired XML file and change the value of it. XSLT or Microsoft XML Document Transform (http://msdn.microsoft.com/en-us/library/dd465326(VS.100).aspx) can be used.
Let's change the values on NinjectInjection.Release.xml file.

 <?xml version="1.0" encoding="utf-8" ?>  
 <!-- For more information on using transformations   
    see the web.config examples at http://go.microsoft.com/fwlink/?LinkId=214134. -->  
 <module xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">  
  <bind  
   service="MyProject.Interface.Cache.ICacheWrapper, MyProject.Interface"  
   to="MyProject.Core.Caching.AzureCacheWrapper, MyProject.Core"  
   xdt:Transform="SetAttributes" xdt:Locator="Match(service)"/>  
  <bind  
   service="MyProject.Interface.Cache.IAppCache, MyProject.Interface"  
   to="MyProject.Core.Caching.AzureAppCache, MyProject.Core"  
   xdt:Transform="SetAttributes" xdt:Locator="Match(service)"/>  
  <bind  
   service="MyProject.Interface.Uploader.IFileUpload, MyProject.Interface"  
   to="MyProject.Core.Uploader.Azure.AzureFileUpload, MyProject.Core"  
   xdt:Transform="SetAttributes" xdt:Locator="Match(service)"/>  
 </module>  

xdt:Locator="Match(service)" is to find element with specified attribute value and xdt:Transform="SetAttributes" to set new value.

We can check transformation text by right clicking NinjectInjection.Release.xml file and selecting Preview Transform which will result as:
XML Transformation Preview


Step 3 - Setting up Ninject kernel to load injections through XML file:

Let's first configure XML file to move into project's bin directory on successful build of application. Right click NinjectInjection.xml file and select Properties to set Copy to Output Directory as Copy to always or Copy to newer.














This will always get transformed XML file based on build configuration profile.

Now, just registration need to be done on Ninject kernel. Ideally, NinjectWebCommon file gets created under App_Start folder. On RegisterServices function put these to configure kernel.

       kernel.Load(Assembly.GetExecutingAssembly());  
       var ninjectConfig = Path.Combine(AppDomain.CurrentDomain.SetupInformation.ApplicationBase, "bin//NinjectInjection.xml");  
       if (File.Exists(ninjectConfig))  
       {  
         kernel.Load(ninjectConfig);  
       }  

The above code will look into bin directory by name of NinjectInjection.xml and configure kernel. Based on build configuration profile selection, contents of this file will keep changing.

Popular posts from this blog

Architecture solution composting Repository Pattern, Unit Of Work, Dependency Injection, Factory Pattern and others

Project architecture is like garden, we plant the things in certain order and eventually they grow in similar manner. If things are planted well then they will all look(work) great and easier to manage. If they grow as cumbersome it would difficult to maintain and with time more problems would be happening in maintenance.

There is no any fixed or known approach to decide project architecture and specially with Agile Methodology. In Agile Methodology, we cannot predict how our end products will look like similarly we cannot say a certain architecture will fit well for entire development lifespan for project. So, the best thing is to modify the architecture as per our application growth. I understand that it sounds good but will be far more problematic with actual development. If it is left as it is then more problems will arise with time. Just think about moving plant vs a full grown tree.

Coming to technical side, In this article, I will be explaining about the various techniques tha…

LDAP with ASP.Net Identity Core in MVC with project.json

Lightweight Directory Access Protocol (LDAP), the name itself explain it. An application protocol used over an IP network to access the distributed directory information service.

The first and foremost thing is to add references for consuming LDAP. This has to be done by adding reference from Global Assembly Cache (GAC) into project.json

"frameworks": { "net461": { "frameworkAssemblies": { "System.DirectoryServices": "4.0.0.0", "System.DirectoryServices.AccountManagement": "4.0.0.0" } } },
These System.DirectoryServices and System.DirectoryServices.AccountManagement references are used to consume LDAP functionality.

It is always better to have an abstraction for irrelevant items in consuming part. For an example, the application does not need to know about PrincipalContext or any other dependent items from those two references to make it extensible. So, we can begin with some bas…

Configuring Ninject, Asp.Net Identity UserManager, DataProtectorTokenProvider with Owin

It can be bit tricky to configure both Ninject and Asp.Net Identity UserManager if some value is expected from DI to configure UserManager. We will look into configuring both and also use OwinContext to get UserManager.

As usual, all configuration need to be done on Startup.cs. It is just a convention but can be used with different name, the important thing is to decorate class with following attribute to make it Owin start-up:

[assembly: OwinStartup(typeof(MyProject.Web.Startup))]
Ninject configuration

Configuring Ninject kernel through method which would be used to register under Owin.

Startup.cs
public IKernel CreateKernel() { var kernel = new StandardKernel(); try { //kernel.Bind<IHttpModule>().To<HttpApplicationInitializationHttpModule>(); // TODO: Put any other injection which are required. return kernel; } catch { kernel.Dispose(); throw; }…