tsJensen

A quest for software excellence...

DomainAspects: Aspect Oriented Library Update - Configuration by Code and Convention

A year ago I posted a library that I enjoy using in one form or another called DomainAspects, an aspect oriented infrastructure or template for domain driven design in .NET applications. The library allows you to isolate cross cutting concerns such as exception logging and authorization from domain or business specific concerns. I promised to write more about the library but I got distracted with work and other topics.

In this post, I will introduce a new version of the library in which I mark the domain classes internal in order to isolate the implementation of the domain interface from the outside world making it impossible to create an instance of the domain implemenation directly. This change helps to enforce the use of the DomainAspects proxy wrapper to create and dispose of the domain object.

internal class ClassroomDomain : IClassroomDomain
{
  public List<string> GetStudents()
  {
    return new List<string>();
  }
}

I also wanted to explore the idea of getting away from XML configuration in part because Castle Project shuns it while supporting it for backward compatibility and in part because managing runtime configuration files can be problematic and convention is generally easier to support. Here's the aspect oriented service components being registered in the DomainFactory's static constructor:

container = new WindsorContainer(); //no more XML

container.Register(
  Component.For<IPrincipalProvider>()
  .ImplementedBy<PrincipalProvider>()
  .Named("PrincipalProvider")
  .LifeStyle.Transient,
  
  Component.For<IOperationAuthorizer>()
  .ImplementedBy<OperationAuthorizer>()
  .Named("OperationAuthorizer")
  .LifeStyle.Transient,
  
  Component.For<IOperationAuditor>()
  .ImplementedBy<OperationAuditor>()
  .Named("OperationAuditor")
  .LifeStyle.Transient,
  
  Component.For<OperationInterceptor>()
  .Named("OperationInterceptor")
  .LifeStyle.Transient);

Now, the DomainFactory's Create method uses the convention that the implementation has the same name without the "I" prefix on the interface name.

/// <summary>
/// Use this factory method to create a transient (one time use) instance.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <returns></returns>
public static T Create<T>() where T : class
{
  var svc = container.GetService<T>();
  if (null == svc)
  {
    //resolution of type by convention MyClass implements IMyClass
    Type interfaceType = typeof(T);
    var implementedByName = interfaceType.AssemblyQualifiedName
      .Replace("." + interfaceType.Name + ",",
					"." + interfaceType.Name.Substring(1) + ",");
    Type implementedByType = Type.GetType(implementedByName);
    if (null == implementedByType) 
      throw new TypeAccessException(string.Format("Type {0} could not be found.", implementedByName));

    container.Register(Component.For(interfaceType)
      .ImplementedBy(implementedByType)
      .Named(implementedByType.Name)
      .Interceptors(InterceptorReference.ForKey("OperationInterceptor")).Anywhere
      .LifeStyle.Transient);
  }
  if (!isConfigured) throw initializationException;
  return container.Resolve<T>();
}

Now I remove the app.config from my projects and run my tests XML-config-free. There is a lot more fun stuff to explore in this library, so check back soon for more info on DomainAspects.

You can download the new code here: DomainAspects_v1_1.zip (30.25 KB).