Where Should I Register Objects in a Multi-Layered Castle Windsor Application for Optimal Design and Testability?

The best place and method to register objects in a multi-level Castle Windsor application

When integrating Castle Windsor into an application with a multi-layer structure (such as a data access layer, a business logic layer, and an application layer), it is important to carefully consider the design of the object registration in Windsor. The question is: who should be responsible for registering objects?

Design plan for object registration

1. Each layer registers itself: Each layer registers its own objects. For example, the business logic layer registers data access layer components, while the testbench for the business logic layer replaces the data access layer with mock classes.
2. Dependency registration: Each layer registers its dependencies, for example, the business logic layer registers the data access layer component. Testing will involve unloading the "real" data access layer objects and replacing them with mock objects.
3. Application-Level Registration: The application (or test application) is responsible for registering objects for all dependencies.

Recommended method: Combination roots

To achieve maximum modularity and loose coupling, all application components should be composed as late as possible. In practice, this means configuring the container at the root of the application:

• Desktop App: Main How to
• ASP.NET Application: Global.asax
• WCF Application: ServiceHostFactory

The

container acts as the composition engine and the application root acts as the composition root . This ensures that the application remains a simple executable without unnecessary unit testing.

Testing without containers

Testing should avoid relying on containers. Instead, objects and modules should be designed to be container-agnostic. Unit tests can directly provide test doubles for these components.

Windsor installer is used to package

In Windsor, component registration logic can be encapsulated in an installer that implements IWindsorInstaller. See the Windsor documentation for more details.

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