How to overwrite a component with castle windsor?

Question

I want to redefine an (default) implementation in a given windsor-container. Is that what OverWrite is for? Doesn't work, though.

container.Register(
                    Component.For<IServiceOperationAuthorization>()
                            .OverWrite()
                            .Instance(_authorization)
                    );

Any other Ideas?

cheers, Lars

Answer 1

I actually found a nice solution where I combine xml-files for overrides and use fluent registrations for defaults.

The fluent-API takes the fullname of a impl as the default key. On the fly I override the id's of the xml-config to imitate the key-conventions of the fluent-API.

Then i register the xml-config while I listen to Kernel.ComponentRegistered.

Afterwards I only add services from the code-config where the xml hasn't yet defined the service.

(it's a while ago and I just copy-pasted the code. hopefully you get it working. I'll do edits if you find any problems)

IList<Type> unnamedServices = new List<Type>();
IDictionary<string, Type> namedServices = new Dictionary<string, Type>();

ComponentDataDelegate registered = captureRegistrations(unnamedServices, namedServices);

container.Kernel.ComponentRegistered += registered;

// The method that captures the services
private static ComponentDataDelegate captureRegistrations(
    IList<Type> unnamedServices, IDictionary<string, Type> namedServices)
{
        return (key, handler) =>
               {
                   if (handler.ComponentModel.Name == handler.ComponentModel.Implementation.FullName)
                   {
                       unnamedServices.Add(handler.Service);
                   }
                   else
                   {
                       namedServices.Add(key, handler.Service);
                   }
               };
}

After that before I register services in code, I check if they already have been registered. I also created a base class that makes this more easy. This is an application configuration:

public class ApplicationConfiguration : WindsorConfigurationSkeleton
{
    internal static WindsorServiceLocator create()
    {
        var container = createWith(null, "components-config.xml", coreServices, caches, roles);
        return new WindsorServiceLocator(container);
    }

    internal static IEnumerable<IRegistration> coreServices()
    {
        yield return Component.For<ISystemClock>()
            .ImplementedBy<PreciseSystemClock>()
            .Parameters(Parameter.ForKey("synchronizePeriodSeconds").Eq("10"))
            .LifeStyle.Singleton;

        yield return Component.For<IMailService>()
            .ImplementedBy<MailQueueService>()
            .LifeStyle.Singleton;
    }

    internal static IEnumerable<IRegistration> caches()
    {
        yield return Component.For<IDataCache<ServiceAttributes>>()
            .ImplementedBy<NoDataCache<ServiceAttributes>>()
            .LifeStyle.Singleton;

        // ....
    }
}

The base class that does the wiring: (Logging is from Commons.Logging)

public class WindsorConfigurationSkeleton
{
    private static readonly ILog _log = LogManager.GetLogger(
        typeof(WindsorConfigurationSkeleton));

    internal static IWindsorContainer createWith(
        IRegistration[] customs, string configFile, params Func<IEnumerable<IRegistration>>[] methods)
    {
        IWindsorContainer container = new WindsorContainer();
        BugFix.Kernel = container.Kernel;

        container.AddFacility("factory.support", new FactorySupportFacility());

        IList<Type> unnamedServices = new List<Type>();
        IDictionary<string, Type> namedServices = new Dictionary<string, Type>();

        ComponentDataDelegate registered = captureRegistrations(unnamedServices, namedServices);

        container.Kernel.ComponentRegistered += registered;

        if (customs != null)
        {
            container.Register(customs);
        }

        if (configFile != null)
        {
            tryAddXmlConfig(container, configFile);
        }

        container.Kernel.ComponentRegistered -= registered;

        if (methods != null && methods.Length > 0)
        {
            container.Register(union(unnamedServices, namedServices, methods));
        }

        return container;
    }

    private static ComponentDataDelegate captureRegistrations(
        IList<Type> unnamedServices, IDictionary<string, Type> namedServices)
    {
        return (key, handler) =>
               {
                   if (handler.ComponentModel.Name == handler.ComponentModel.Implementation.FullName)
                   {
                        var text = unnamedServices.Contains(handler.Service) ? "another" : "default";
                       _log.Info(
                           m => m(
                                    "Registered {2} service for {0} with {1}.",
                                    handler.Service.GetDisplayName(),
                                    handler.ComponentModel.Implementation.GetDisplayName(),
                                    text
                                    ));

                       unnamedServices.Add(handler.Service);
                   }
                   else
                   {
                        var text = namedServices.ContainsKey(key) ? "another" : "default";
                       _log.Info(
                           m => m(
                                    "Registered {3} service {0} with name '{1}' and {2}.",
                                    handler.ComponentModel.Service,
                                    handler.ComponentModel.Name,
                                    handler.ComponentModel.Implementation.GetDisplayName(),
                                    text
                                    ));
                       namedServices.Add(key, handler.Service);
                   }
               };
    }

    protected static void tryAddXmlConfig(IWindsorContainer container, string filename)
    {
        var fi = Resources.GetFileFromResourceHierarchy(typeof(ApplicationContext).Namespace, filename);
        if ( fi == null ) {
            return;
        }
        var configFile = fi.FullName;
        var xd = immitateFluentApiDefaultIdBehaviour(configFile);
        container.Install(Configuration.FromXml(new StaticContentResource(xd.OuterXml)));

    }

    private static XmlDocument immitateFluentApiDefaultIdBehaviour(string configFile)
    {
        var xd = new XmlDocument();
        xd.Load(configFile);

        foreach (
            XmlElement component in
                xd.SelectNodes("/configuration/components/component[@type and (not(@id) or @id = '')]"))
        {
            var type = Type.GetType(component.GetAttribute("type"), true);
            component.SetAttribute("id", type.FullName);
        }

        return xd;
    }

    private static IRegistration[] union(
        IList<Type> unnamed, IDictionary<string, Type> named, params Func<IEnumerable<IRegistration>>[] methods)
    {
        var all = new List<IRegistration>();
        foreach (var method in methods)
        {
            foreach (var registration in method())
            {
                var registrationType = registration.GetType();
                if (registrationType.IsGenericTypeOf(typeof(ComponentRegistration<>)))
                {
                    var componentType = registrationType.GetGenericArgumentsFor(typeof(ComponentRegistration<>))[0];

                    var name = (string)registrationType.GetProperty("Name").GetValue(registration, null);

                    if (name != null)
                    {
                        if (named.ContainsKey(name))
                        {
                            _log.Debug(
                                m => m("Skipped registering default named component {0}.", name));
                            continue;
                        }
                    }
                    else if (unnamed.Contains(componentType))
                    {
                        _log.Debug(
                            m => m("Skipped registering default component for type {0}.", componentType));
                        continue;
                    }

                    all.Add(registration);
                }
                else
                {
                    all.Add(registration);
                }
            }
        }

        return all.ToArray();
    }
}

Answer 2

You could very simply do this in the place you need to override the default implementation. This is an example from our integration tests. Both implementations are now registered but your code will use the default one, which is the one you've just registered. Works like a bomb and doesn't have any impact on the rest of the application:

        var sendMailStub = MockRepository.GenerateStub<ISendMail>();
        _container.Register(
            Component
                .For<ISendMail>()
                .Instance(sendMailStub)
                .IsDefault()
            );

Answer 3

I agree with Krzysztof that this is usually not a good idea... However as far as I can tell OverWrite() does not overwrite the default component, it just overwrites the lifestyle defined by attribute (i.e. [Singleton]).

If you want to replace a component, you can use container.Kernel.RemoveComponent(string key) followed by the registration of the new component.

Here's an example where this does make sense.

Answer 4

I needed to switch a component implementation when running a system in a integration test suite and failed to use container.Kernel.RemoveComponent(). So I ended up with a simple facility which takes care of this for me.

Answer 5

This would be the kind of problem that might be better solved by setting the container up with a decorator, where you can explicitly change the implementation the decorator is directing calls to ... especially if you want to replace the implementation that existing components (i.e. singletons) have been injected with which might exist for the lifetime of your application.

Really need more background on what you're trying to achieve.

---

Here is more information about registering Decorators with Windsor.

Answer 6

Yes, it does redefine default implementation of a service. Why do you do this? Why not register this in the first place, instead of redefining it?

Could you provide more context?