On most of my projects I'm using Autofac as the Inversion of Control container of my choice. However this introduces an extra dependency and it comes with a (although short) learning curve. So o a newer project, I decided to give the built-in IoC container in .NET Core another try.
The standard DI stuff worked as expected, however there was one situation where I had to investigate a little further. Let me explain...
Registering multiple implementations for the same interface
Here is my use case; in my application I’m using Serilog. One of the features that Serilog has to offer is the concept of an enricher. This allows you to enrich your log messages with extra information in an easy way. As some of my enrichers required dependencies I wanted to register those enrichers in my IoC container.
When using Autofac I would have done this like this:
To do the same thing using the Microsoft DI container is not that different:
The AddTransient() method will not override an existing registration allowing us to register multiple implementations for the same interface.
Remark: If you want to have only one implementation registered for a specific interface, you can use the TryAdd… methods available as part of the Microsoft.Extensions.DependencyInjection.Extensions namespace.
Resolving multiple implementations for the same interface
Ok, that was not that hard. How can we now resolve these implementations?
What is not possible is to resolve a specific implementation as there is no support for keyed or named services. (Have a look here if you want to see how can be done suing Autofac).
Luckily in this case I wanted to get ALL implementations back. That can be done by resolving an IEnumerable<IRegisteredInterface> instance. This will load all registered implementations from the DI container.
Nice!