Autofac - Decorators

One of the nice features of Autofac is the support for decorators.

A decorator class implements the same interface as the class it “wraps”.  With a decorator you can add functionality to a class without changing it’s signature.

Let’s walk through an example step by step:

Here is the class and it’s corresponding interface I want to decorate:

	public class ConsoleLogger: ILogger
	{
	public Task LogInformation(string message)
	{
	Console.WriteLine(message);
	}
	}

view raw ConsoleLogger.cs hosted with ❤ by GitHub

	public interface ILogger
	{
	Task LogInformation(string message);
	}

view raw ILogger.cs hosted with ❤ by GitHub

Nothing special at the Autofac level yet:

builder.RegisterType<ConsoleLogger>().As<ILogger>();

view raw RegisterConsoleLogger.cs hosted with ❤ by GitHub

Let’s now extend the behavior of this class through a decorator. What if we want to benchmark the execution time of the LogMessage() method? The decorator class should implement the same interface AND inject the interface at the same time:

	public class BenchmarkDecorator:ILogger
	{
	private readonly ILogger _decoratedLogger;
	public BenchmarkDecorator(ILogger logger)
	{
	_decoratedLogger=logger;
	}
	public async Task LogMessage(string message)
	{
	//Add your benchmark logic here
	await _decoratedLogger.LogMessage(message);
	//And here :-)
	}
	}

view raw ILoggerDecorator.cs hosted with ❤ by GitHub

Now we need to register the decorator in Autofac:

builder.RegisterDecorator<ILoggerDecorator,ILogger();

view raw RegisterDecorator.cs hosted with ❤ by GitHub

Remark: When using generics, it is also possible to register an open generic  decorator. Therefore you need to use the RegisterGenericDecorator() overload

More information: https://autofaccn.readthedocs.io/en/latest/advanced/adapters-decorators.html