ExamplesContextBasedResolution.md

Examples of context based resolution

• Examples of context based resolution
  • log4net logger
  • Serilog logger

log4net logger

Here is the discussion and example how to inject log4net in Autofac.

In DryIoc we may use strongly-typed Factory Method specification to register log4net.ILog:

namespace DryIoc.Docs;
using DryIoc;
using NUnit.Framework;
using System;
using log4net;

class Log4net_logger_example
{
    public class A
    {
        public ILog Logger { get; }
        public A(ILog logger)
        {
            Logger = logger;
        }
    }

    [Test]
    public void Example()
    {
        var container = new Container();
        container.Register<A>();

        container.Register(Made.Of<ILog>(() => 
                LogManager.GetLogger(Arg.Index<string>(0)),
                request => request.Parent.ImplementationType.Name.ToString()));

        var a = container.Resolve<A>();
        Assert.IsNotNull(a.Logger);
    }
} 

Made.Of Arg.Index<Type>(0) argument references to the value: request => request.Parent.ImplementationType, which evaluates to the typeof(A) in the example.

Serilog logger

The code is similar to the log4net with using dependency parent type as context for instantiating of ILogger. In addition, the condition allows to use default logger where context is not available, e.g. at resolution root.

class Serilog_logger_example
{
    public class LogSubject
    {
        public Serilog.ILogger Logger { get; }
        public LogSubject(Serilog.ILogger logger)
        {
            Logger = logger;
        }
    }

    [Test]
    public void Example()
    {
        var container = new Container();

        // default logger
        container.Register(Made.Of(() => Serilog.Log.Logger),
            setup: Setup.With(condition: r => r.Parent.ImplementationType == null));

        // type dependent logger
        container.Register(
            Made.Of(() => Serilog.Log.ForContext(Arg.Index<Type>(0)), r => r.Parent.ImplementationType),
            setup: Setup.With(condition: r => r.Parent.ImplementationType != null));

        var defaultLogger = container.Resolve<Serilog.ILogger>();
        Assert.AreSame(Serilog.Log.Logger, defaultLogger);

        container.Register<LogSubject>();
        var s = container.Resolve<LogSubject>();

        Assert.AreSame(Serilog.Log.ForContext<LogSubject>(), s.Logger);
    }
}