Bobbysoft.Extensions.DependencyInjection.Decoration 1.1.4

Bobbysoft.Extensions.DependencyInjection.ServiceDecoration

ServiceDecorator

This light weight class library is used to decorate already dependency injected classes inside the Microsoft.Extensions.DependencyInjection.IServiceCollection.

The quick overview

using Bobbysoft.Extensions.DependencyInjection;

public void DecorateServices(IServiceCollection services)
{

  // ***ServiceDecorator.Decorate is the extension method added with this Library
  services.Decorate<ILogger>(
    subject => new LoggerDecorator(subject));
}

using Bobbysoft.Extensions.DependencyInjection;

public void DecorateServices(IServiceCollection services)
{

  // ***ServiceDecorator.Decorate is the extension method added with this Library
  services.Decorate<ILogger>(
    (subject, provider) => new LoggerDecorator(subject, provider.GetRequiredService<Emailer>()));
}

Step 1: make sure you know what a decorator is

• GOF Decorator Design pattern
• Excellent explanation by Shiv Kumar youtube

Step 2: decide which class to decorate

I choose the SeriLogger from SeriLog that is registered with the ILogger interface. It does not matter if the interface is an abstract class interface or an c#-Interface-Interface I could have picked any of the two for this tutorial.

Step 3: write a decorator to the chosen abstraction

internal class LoggerDecorator : ILogger
{
    private readonly ILogger _logger;
    public LoggerDecorator(ILogger logger)
    {
        _logger = logger;
    }

    public void Write(LogEvent logEvent)
    {
        DecorateLogEvent(logEvent);
        _logger.Write(logEvent);
    }

    private void DecorateLogEvent(LogEvent logEvent)
    {
        // Decorate your logEvent here
    }
}

Step 4: Register both Service (abstraction) and implementation in the IServiceCollection

public void ConfigureServices(IServiceCollection services)
{

  services.AddLogging(loggingBuilder =>
    loggingBuilder.AddSerilog(dispose: true));

      // Other services ...
}

Step 5: Decorate the ServiceCollection from the outside of the IServiceCollection

using Bobbysoft.Extensions.DependencyInjection;

public void DecorateServices(IServiceCollection services)
{

  // ***ServiceDecorator.Decorate is the extension method added with this Library
  services.Decorate<ILogger>(
    subject => new LoggerDecorator(subject));
}

The other way - with multiple dependencies

Add a modified decorator

internal class LoggerDecorator : ILogger
{
    private readonly ILogger _logger;
    private readonly Emailer _emailer;

    // We are adding a second dependency Emailer
    public LoggerDecorator(ILogger logger, Emailer emailer)
    {
        _logger = logger;
        _emailer = emailer;
    }

    public void Write(LogEvent logEvent)
    {
        DecorateLogEvent(logEvent);
        _emailer.Send(logEvent);
        _logger.Write(logEvent);
    }

    private void DecorateLogEvent(LogEvent logEvent)
    {
        // Decorate your logEvent here
    }
}

Register both implementations services

using Bobbysoft.Extensions.DependencyInjection;

public void ConfigureServices(IServiceCollection services)
{

  services.AddLogging(loggingBuilder =>
    loggingBuilder.AddSerilog(dispose: true));

  services.AddTransient<Emailer>();
      // Other services ...
}

public void DecorateServices(IServiceCollection services)
{

  // ***ServiceDecorator.Decorate is the extension method added with this Library
  services.Decorate<ILogger>(
    (subject, provider) => new LoggerDecorator(subject, provider.GetService<Emailer>()));
}

If in doubt look at the different examples in the test project