CastleWindsor chained dependency

Source code is available here.

I recently had a problem where I wanted an MVC controller to use constructor injection of specified dependency and have that dependency load another specified dependency using Windsor.

For example, I have a message of the day controller and it can get messages from either a file or from a database. To support this I have a message of the day service which formats the text it retrieves from a message of the day loader.

But as I said I have two ways of loading the message, so for the sake of this demo I have two services and two loaders.

I don’t want my controller to request a named instance, I just want to register the implementations in the installers and let Windsor do the rest.

If the controller is using the database service, I want the database service to use the database loader; if the controller is using the file service, I want the file service to use the file loader.

To support this I added a ContractInstaller as shown here.

 1public class ContractInstaller : IWindsorInstaller
 2{
 3    public void Install(IWindsorContainer container, IConfigurationStore store)
 4    {
 5        container.Register(
 6                Component.For<IMessageLoader>().ImplementedBy<MessageLoaderDatabase>()
 7            ,Component.For<IMessageLoader>().ImplementedBy<MessageLoaderFile>()
 8
 9            ,Component.For<IMessageOfTheDayService>().ImplementedBy<MessageOfTheDayServiceDatabase>()
10                .DependsOn(Dependency.OnComponent<IMessageLoader, MessageLoaderDatabase>())
11
12            ,Component.For<IMessageOfTheDayService>().ImplementedBy<MessageOfTheDayServiceFile>()
13                .DependsOn(Dependency.OnComponent<IMessageLoader, MessageLoaderFile>())
14
15            ,Component.For<MessageOfTheDayController>().LifestyleTransient()
16                .DependsOn(Dependency.OnComponent<IMessageOfTheDayService, MessageOfTheDayServiceFile>())
17        );
18    }
19}

• In lines 6 and 7 I register the loaders (IMessageLoader)
• Lines 9 and 12 I register the the services (IMessageOfTheDayService) and they in turn depend on the registered loaders.
• In line 15 I register the controller (MessageOfTheDayController) and its dependency on IMessageOfTheDayService, in this case it is using MessageOfTheDayServiceFile.
• To use the MessageOfTheDayServiceDatabase, change the dependency on line 16.

Be sure to load this before the ControllersInstaller provided by the Windsor nuget or you will get a clash between the MessageOfTheDayController loaded by both installers. To make sure this happens I alter the default Bootstrap method in ContainerBootstrapper to the following.

1public static ContainerBootstrapper Bootstrap()
2{
3    var container = new WindsorContainer().Install(
4        new ContractInstaller(),
5        new ControllersInstaller()
6        );
7
8    return new ContainerBootstrapper(container);
9}

Now when you run the app, the controller will be instantiated with the MessageOfTheDayServiceDatabase which in turn will be instantiated with MessageLoaderDatabase.

Source code is available here.