Composition Root Pattern

I have coded in C# for over 10 years now, and this pattern, used with AspNet, is, in my opinion, the most efficient way to bootstrap a DotNet service.

The Composition Root pattern is a design principle in software architecture that emphasises the centralisation of object creation and dependency resolution in one place, typically at the entry point of an application.

This pattern helps maintain the Separation of Concerns (SoC) by ensuring that application components remain focused on their core responsibilities without worrying about their dependencies’ construction or lifecycle.

Key Characteristics of the Composition Root Pattern

1. Centralised Object Composition

   1. Dependencies are wired together in one place, ensuring consistency in

      how objects are created, and dependencies are injected.

   2. The entire dependency graph is discoverable in one location in the

      application code.

   3. The composition project is a map of how your dependencies are

      constructed, how they interact and how they are resolved.

2. Early Dependency Resolution

   1. Dependencies are resolved during the application’s startup or

      initialisation, which can help identify issues early in the application

      lifecycle.

   2. The container has all the configuration necessary to build all the

      dependencies.

3. Inversion of Control (IoC)

   1. Aligns with the IoC principle, where the responsibility for creating

      objects is delegated to a dedicated structure (e.g., a dependency

      injection container).

4. Flexibility and Testability

   1. By centralising dependency configuration, you can easily swap

      implementations (e.g., for testing purposes or different environments)

      without modifying the dependent code.

5. Minimal Application Logic

   1. The composition root typically contains no application logic. It solely

      focuses on creating and assembling object graphs.

6. Predictable Dependency Graph

   1. All calls to the project should have a pre-constructed, pre-discovered

      dependency chain.

   2. No dependencies are built on-the-fly.