SAF Dependency Injection (DI) Container Overview

The Smart Application Framework (SAF) utilizes Microsoft’s .NET Core Dependency Injection to provide a main Dependency Injection (DI) container that loads various plug-ins. At its base, it provides exchangeable messaging and storage infrastructure services as well as a logging interface.

When starting to implement a SAF Host you are required to build the SAF main DI container by adding the SAF Service Host and your required SAF Infrastructure Services using the provided extension methods for the Microsoft DIs IServiceCollection interface as shown in the following exemplary code snippet:

var applicationServices = new ServiceCollection();
applicationServices.AddHost(config => {}, null);
applicationServices.AddCdeInfrastructure(cdeConfig => {});

using var applicationServiceProvider = applicationServices.BuildServiceProvider();
applicationServiceProvider.UseServiceHost();

This code builds the main DI container by adding the SAF ServiceHost and the C-DEngine specific infrastructure service implementations. In addition it loads available SAF Plug-ins. While loading the SAF Plug-ins, SAF internally creates one independent DI container for each of them. It registers the infrastructure services added to the main DI container to the independent Plug-in specific DI container. With that the added SAF infrastructure can be used inside the loaded SAF Plug-ins.

Additionaly the SAF Service Host calls the Plug-ins IServiceAssemblyManifest.RegisterDependencies method. Inside this method the SAF Plug-in is allowed to register any type at the SAF Plug-in specific DI container that is needed inside the Plug-in itself. This could also be any of the SAF Toolbox Services which also provide extension methods for being added to the DI container.

All services registered to the Plug-in specific DI container are isolated in that container and are therefore not accessible from inside other Plug-ins. Plug-in to Plug-in communication is therefore only possible through the messaging infrastructure service registered in the main DI container.

Afterwards the code snippet above runs the SAF application by calling the UserServiceHost extension method.

The following diagram shows the existing DI containers inside a SAF application:

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The Main Container stores the Infrastructure Services that are shared with the Plug-ins because they are added to the Plug-in specific DI containers as well.
The Plug-in specific containers Plug-in Container 1 and Plug-in Container 2 store the same Infrastructure Services and in addition the Plug-in specific services registered inside the IServiceAssemblyManifest.RegisterDependencies call.

This ensures to share the same Infrastructure Services with all plug-ins, whereas the Plug-in specific services are isolated from each other and can only be used inside the Plug-in itself.