Dru Sellers

Application Instance

320 words · 2 minute read

So, if [IoC is the Context](% post_url 2013-12-09-ioc-as-context %}) how do we leverage this concept so we can package it up nicely in our code bases. The goal is to use this context to unlock new aspects.

I have an application factory class that generates application instances.

The factory is responsible for bootstrapping the logging, doing all of the assembly scanning, then passes a [TypePool](% post_url 2014-09-10-typepool %}) and the container into the application.

{{< highlight csharp >}} public static class AppFactory { public static Application Build<TApplication>() where TApplication : ApplicationMarker, new() { //boot strap logging

var pool = new TypePool(); //collect all assemblies for this host

var container = new Container(); //build up container

return new ApplicationInstance(container, pool);

} } {{< /highlight >}}

The application instance looks like this

{{< highlight csharp >}} public interface Application : IDisposable { void Start(); TComponent Resolve<TComponent>(); void Scope(Action<ILifetimeScope> action); void Dispatch(Request request); } {{< /highlight >}}

The Start method looks like

{{< highlight csharp >}} public class ApplicationInstance : Application { public void Start() { //run db migrations

//run all bootup code


//other stuff } {{< /highlight >}}

The ApplicationMarker looks like

{{< highlight csharp >}} public interface ApplicationMarker { void ConfigureContainer(TypePool pool, ContainerBuilder builder); } {{< /highlight >}}

Benefits include super simple testing a predictable and shared common architecture across command line apps web apps / messaging apps (this is very nice for larger companies)

In integration tests I can say things like:

{{< highlight csharp >}} public class SampleTest { [Test] public void Test() { var app = AppFactory.Build<MyApplication>(); var sut = app.Resolve<TheSystemToTest>(); var result = sut.TheMethodToTest(some, parameters); result.ShouldNotBeNull(); } } {{< /highlight >}}

Now I know that my app instance is the same as how its going to be built in in test as it is in the application host.