TryAtSoftware.Extensions.DependencyInjection.md

About the project

TryAtSoftware.Extensions.DependencyInjection is a library containing extension methods and utility components that should simplify some common operations with dependency injection.

About us

Try At Software is a software development company based in Bulgaria. We are mainly using dotnet technologies (C#, ASP.NET Core, Entity Framework Core, etc.) and our main idea is to provide a set of tools that can simplify the majority of work a developer does on a daily basis.

Getting started

Installing the package

In order to use this library, you need to install the corresponding NuGet package beforehand. The simplest way to do this is to either use the NuGet package manager, or the dotnet CLI.

Using the NuGet package manager console within Visual Studio, you can install the package using the following command:

Install-Package TryAtSoftware.Extensions.DependencyInjection

Or using the dotnet CLI from a terminal window:

dotnet add package TryAtSoftware.Extensions.DependencyInjection

Registering services

The TryAtSoftware.Extensions.DependencyInjection library supports automatic registration of services into a dependency injection container. This can be realized throughout the AutoRegisterServices extension method. It will locate all classes decorated with the AutomaticallyRegisteredService attribute and register them as services using a concrete implementation of the IServiceRegistrar interface.

Service configuration

As mentioned in the previous paragraph, there is an attribute used to decorate all services. It implies that the decorated class should be treated as a component that is expected to be registered automatically into the dependency injection container.

[AutomaticallyRegisteredService]
public class EmailSender : IEmailSender
{
    // Here goes the implementation of the email sender... 
}

Each concrete implementation of the IServiceRegistrar interface may propose its own alternative (platform-specific) configuration options and mechanisms.

Use cases

Register services from all assemblies

IServiceRegistrar serviceRegistrar = PrepareServiceRegistrar();
Assembly[] allAssemblies = AppDomain.CurrentDomain.GetAssemblies();

allAssemblies.AutoRegisterServices(serviceRegistrar);

It is important to note that the AppDomain.CurrentDomain.GetAssemblies() invocation will return only those assemblies that are already loaded for the current domain. If some of the assemblies containing services that are expected to be registered automatically are not returned, they should be loaded explicitly.

This problem can be solved easily if the assembly extension methods provided by TryAtSoftware.Extensions.Reflection are used (for more information, you can refer to the official documentation).

// It is recommended to use a `RestrictSearchFilter` in order to load only what is necessary.
var options = new LoadReferencedAssembliesOptions { RestrictSearchFilter = x => x.FullName.StartsWith("My.Awesome.Prefix")};
Assembly.GetExecutingAssembly().LoadReferencedAssemblies(options);

IServiceRegistrar serviceRegistrar = PrepareServiceRegistrar();
Assembly[] allAssemblies = AppDomain.CurrentDomain.GetAssemblies();

allAssemblies.AutoRegisterServices(serviceRegistrar);

Resolve generic parameters

A key feature for the automatic registration of services is the ability to resolve generic type parameters. This is a responsibility of each IServiceRegistrar implementation, however, all officially supported service registrars use the generic extension methods provided by TryAtSoftware.Extensions.Reflection (for more information you can refer to the official documentation).

The service configuration needs to be extended by decorating every generic type parameter with a custom attribute.

[AttributeUsage(AttributeTargets.GenericParameter)]
public class KeyTypeAttribute : Attribute {}

public class StorageService<[KeyType] TKey> : IStorageService<TKey> {}

Having this setup, the only other thing that needs to be done, is to indicate how a generic type parameter decorated with a given attribute should be resolved. For this purpose, we can extend the AutoRegisterServices invocation by providing an additional RegisterServiceOptions instance (GenericTypesMap is the related property).

IServiceRegistrar serviceRegistrar = PrepareServiceRegistrar();
Assembly[] allAssemblies = AppDomain.CurrentDomain.GetAssemblies();

RegisterServiceOptions registrationOptions = new RegisterServiceOptions { GenericTypesMap = new Dictionary<Type, Type> { [typeof(KeyTypeAttribute)] = typeof(Guid) } };
allAssemblies.AutoRegisterServices(serviceRegistrar, registrationOptions);

IServiceRegistrar

This is an interface defining the structure of a component responsible for registering services into a dependency injection container.

The officially supported libraries providing implementations for this interface will be listed at the home page of the TryAtSoftware.Extensions repository.