Using a Strategy and Factory Pattern with Dependency Injection

Question

I am working on a side project to better understand Inversion of Control and Dependency Injection and different design patterns.

I am wondering if there are

Answer 1

So I did it like this. I would have preferred to have injected an IDictionary, but because of the limitation with injecting "IEnumerable" into the constructor (this limitation is Unity specific), I came up with a little workaround.

public interface IShipper
{
    void ShipOrder(Order ord);

    string FriendlyNameInstance { get;} /* here for my "trick" */
}

..

public interface IOrderProcessor
{
    void ProcessOrder(String preferredShipperAbbreviation, Order ord);
}

..

public class Order
{
}

..

public class FedExShipper : IShipper
{
    private readonly Common.Logging.ILog logger;

    public static readonly string FriendlyName = typeof(FedExShipper).FullName; /* here for my "trick" */

    public FedExShipper(Common.Logging.ILog lgr)
    {
        if (null == lgr)
        {
            throw new ArgumentOutOfRangeException("Log is null");
        }

        this.logger = lgr;
    }

    public string FriendlyNameInstance => FriendlyName; /* here for my "trick" */

    public void ShipOrder(Order ord)
    {
        this.logger.Info("I'm shipping the Order with FedEx");
    }

..

public class UpsShipper : IShipper
{
    private readonly Common.Logging.ILog logger;

    public static readonly string FriendlyName = typeof(UpsShipper).FullName; /* here for my "trick" */

    public UpsShipper(Common.Logging.ILog lgr)
    {
        if (null == lgr)
        {
            throw new ArgumentOutOfRangeException("Log is null");
        }

        this.logger = lgr;
    }

    public string FriendlyNameInstance => FriendlyName; /* here for my "trick" */

    public void ShipOrder(Order ord)
    {
        this.logger.Info("I'm shipping the Order with Ups");
    }
}

..

public class UspsShipper : IShipper
{
    private readonly Common.Logging.ILog logger;

    public static readonly string FriendlyName = typeof(UspsShipper).FullName; /* here for my "trick" */

    public UspsShipper(Common.Logging.ILog lgr)
    {
        if (null == lgr)
        {
            throw new ArgumentOutOfRangeException("Log is null");
        }

        this.logger = lgr;
    }

    public string FriendlyNameInstance => FriendlyName; /* here for my "trick" */

    public void ShipOrder(Order ord)
    {
        this.logger.Info("I'm shipping the Order with Usps");
    }
}

..

public class OrderProcessor : IOrderProcessor
{
    private Common.Logging.ILog logger;
    //IDictionary shippers; /*   :(    I couldn't get IDictionary  to work */
    IEnumerable shippers;

    public OrderProcessor(Common.Logging.ILog lgr, IEnumerable shprs)
    {
        if (null == lgr)
        {
            throw new ArgumentOutOfRangeException("Log is null");
        }

        if (null == shprs)
        {
            throw new ArgumentOutOfRangeException("ShipperInterface(s) is null");
        }

        this.logger = lgr;
        this.shippers = shprs;
    }

    public void ProcessOrder(String preferredShipperAbbreviation, Order ord)
    {
        this.logger.Info(String.Format("About to ship. ({0})", preferredShipperAbbreviation));

        /* below foreach is not needed, just "proves" everything was injected */
        foreach (IShipper sh in shippers)
        {
            this.logger.Info(String.Format("ShipperInterface . ({0})", sh.GetType().Name));
        }

        IShipper foundShipper = this.FindIShipper(preferredShipperAbbreviation);
        foundShipper.ShipOrder(ord);
    }


    private IShipper FindIShipper(String preferredShipperAbbreviation)
    {

        IShipper foundShipper = this.shippers.FirstOrDefault(s => s.FriendlyNameInstance.Equals(preferredShipperAbbreviation, StringComparison.OrdinalIgnoreCase));

        if (null == foundShipper)
        {
            throw new ArgumentNullException(
                String.Format("ShipperInterface not found in shipperProviderMap. ('{0}')", preferredShipperAbbreviation));
        }

        return foundShipper;
    }
}

...

And calling code: (that would be in something like "Program.cs" for example)

            Common.Logging.ILog log = Common.Logging.LogManager.GetLogger(typeof(Program));

            IUnityContainer cont = new UnityContainer();

            cont.RegisterInstance(log);

            cont.RegisterType(FedExShipper.FriendlyName);
            cont.RegisterType(UspsShipper.FriendlyName);
            cont.RegisterType(UpsShipper.FriendlyName);

            cont.RegisterType();

            Order ord = new Order();
            IOrderProcessor iop = cont.Resolve();
            iop.ProcessOrder(FedExShipper.FriendlyName, ord);

Logging Output:

2018/09/21 08:13:40:556 [INFO]  MyNamespace.Program - About to ship. (MyNamespace.Bal.Shippers.FedExShipper)
2018/09/21 08:13:40:571 [INFO]  MyNamespace.Program - ShipperInterface . (FedExShipper)
2018/09/21 08:13:40:572 [INFO]  MyNamespace.Program - ShipperInterface . (UspsShipper)
2018/09/21 08:13:40:572 [INFO]  MyNamespace.Program - ShipperInterface . (UpsShipper)
2018/09/21 08:13:40:573 [INFO]  MyNamespace.Program - I'm shipping the Order with FedEx

So each concrete has a static string providing its name in a strong-typed fashion. ("FriendlyName")

And then I have an instance string-get property which uses the exact same value to keep things in sync. ("FriendlyNameInstance")

By forcing the issue by using a property on the Interface (below partial code)

public interface IShipper
{
   string FriendlyNameInstance { get;}
}

I can use this to "find" my shipper out of the collection of shippers.

The internal method "FindIShipper" is the kinda-factory, but removes the need to have a separate IShipperFactory and ShipperFactory interface and class. Thus simplifying the overall setup. And still honors Constructor-Injection and Composition root.

If anyone knows how to use IDictionary (and inject via the constructor), please let me know.

But my solution works...with a little razzle dazzle.

...........................

My third-party-dll dependency list. (I'm using dotnet core, but dotnet framework with a semi new version of Unity should work too). (See PackageReference's below)

  
    Exe
    netcoreapp2.0
  

  
    
    
    
    
    
  

  
    
      Always
    
  

APPEND:

Here is the autofac version:

(using all the same interfaces and concretes above )

Program.cs

namespace MyCompany.ProofOfConcepts.AutofacStrategyPatternExample.DemoCommandLineInterfaceOne
{
    using System;
    using System.Text;
    using Autofac;
    using Autofac.Extensions.DependencyInjection;
    using Microsoft.Extensions.Configuration;
    using Microsoft.Extensions.DependencyInjection;
    using Microsoft.Extensions.Logging;
    /* need usings for all the object above */
    using MyCompany.ProofOfConcepts.AutofacStrategyPatternExample.Domain;
    using NLog;
    using NLog.Extensions.Logging;

    public class Program
    {
        private static Logger programStaticLoggerThatNeedsToBeInitiatedInMainMethod = null;

        public static int Main(string[] args)
        {
            Logger loggerFromNLogLogManagerGetCurrentClassLogger = NLog.LogManager.GetCurrentClassLogger(); /* if this is made a private-static, it does not log the entries */
            programStaticLoggerThatNeedsToBeInitiatedInMainMethod = loggerFromNLogLogManagerGetCurrentClassLogger;

            programStaticLoggerThatNeedsToBeInitiatedInMainMethod.Info("programStaticLoggerThatNeedsToBeInitiatedInMainMethod: Main.Start");
            try
            {
                bool useCodeButNotAutofacJson = true; /* true will "code up" the DI in c# code, false will kick in the autofac.json */

                string autoFacFileName = useCodeButNotAutofacJson ? "autofac.Empty.json" : "autofac.json"; /* use "empty" to prove the DI is not coming from non-empty json */

                programStaticLoggerThatNeedsToBeInitiatedInMainMethod.Info(string.Format("programStaticLoggerThatNeedsToBeInitiatedInMainMethod: autoFacFileName={0}", autoFacFileName));

                IConfiguration config = new ConfigurationBuilder()
                    .SetBasePath(System.IO.Directory.GetCurrentDirectory())
                    .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                    .AddJsonFile(autoFacFileName)
                    .Build();

                IServiceProvider servicesProvider = BuildDi(config, useCodeButNotAutofacJson);
                using (servicesProvider as IDisposable)
                {
                    IOrderProcessor processor = servicesProvider.GetRequiredService();
                    processor.ProcessOrder(FedExShipper.FriendlyName, new Order());

                    Microsoft.Extensions.Logging.ILogger loggerFromIoc = servicesProvider.GetService()
                    .CreateLogger();
                    loggerFromIoc.LogInformation("loggerFromIoc:Starting application");

                    loggerFromIoc.LogInformation("loggerFromIoc:All done!");

                    Console.WriteLine("Press ANY key to exit");
                    Console.ReadLine();
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(GenerateFullFlatMessage(ex));
                //// NLog: catch any exception and log it.
                programStaticLoggerThatNeedsToBeInitiatedInMainMethod.Error(ex, "programStaticLoggerThatNeedsToBeInitiatedInMainMethod : Stopped program because of exception");
                throw;
            }
            finally
            {
                // Ensure to flush and stop internal timers/threads before application-exit (Avoid segmentation fault on Linux)
                LogManager.Shutdown();
            }

            Console.WriteLine("Returning 0 and exiting.");

            return 0;
        }

        private static IServiceProvider BuildDi(IConfiguration config, bool useCodeButNotAutofacJson)
        {
            NLog.Extensions.Logging.NLogProviderOptions nlpopts = new NLog.Extensions.Logging.NLogProviderOptions
            {
                IgnoreEmptyEventId = true,
                CaptureMessageTemplates = true,
                CaptureMessageProperties = true,
                ParseMessageTemplates = true,
                IncludeScopes = true,
                ShutdownOnDispose = true
            };

            IServiceCollection sc = new ServiceCollection()

            ////.AddLogging(loggingBuilder =>
            ////{
            ////    // configure Logging with NLog
            ////    loggingBuilder.ClearProviders();
            ////    loggingBuilder.SetMinimumLevel(Microsoft.Extensions.Logging.LogLevel.Trace);
            ////    loggingBuilder.AddNLog(config);
            ////})

            .AddLogging(loggingBuilder =>
            {
                ////use nlog
                loggingBuilder.AddNLog(nlpopts);
                NLog.LogManager.LoadConfiguration("nlog.config");
            })

            .AddSingleton(config);

            //// // /* before autofac */   return sc.BuildServiceProvider();

            //// Create a container-builder and register dependencies
            Autofac.ContainerBuilder builder = new Autofac.ContainerBuilder();

            // Populate the service-descriptors added to `IServiceCollection`
            // BEFORE you add things to Autofac so that the Autofac
            // registrations can override stuff in the `IServiceCollection`
            // as needed
            builder.Populate(sc);

            if (useCodeButNotAutofacJson)
            {
                programStaticLoggerThatNeedsToBeInitiatedInMainMethod.Info("Coding up Autofac DI");

                /* "Keyed" is not working, do not use below */
                ////builder.RegisterType().Keyed(FedExShipper.FriendlyName);
                ////builder.RegisterType().Keyed(UpsShipper.FriendlyName);
                ////builder.RegisterType().Keyed(UspsShipper.FriendlyName);

                builder.RegisterType().As();
                builder.RegisterType().As();
                builder.RegisterType().As();
                builder.RegisterType().As();
            }
            else
            {
                programStaticLoggerThatNeedsToBeInitiatedInMainMethod.Info("Using .json file to define Autofac DI");

                // Register the ConfigurationModule with Autofac.
                var module = new Autofac.Configuration.ConfigurationModule(config);
                builder.RegisterModule(module);
            }

            Autofac.IContainer autofacContainer = builder.Build();

            // this will be used as the service-provider for the application!
            return new AutofacServiceProvider(autofacContainer);
        }

        private static string GenerateFullFlatMessage(Exception ex)
        {
            return GenerateFullFlatMessage(ex, false);
        }

        private static string GenerateFullFlatMessage(Exception ex, bool showStackTrace)
        {
            string returnValue;

            StringBuilder sb = new StringBuilder();
            Exception nestedEx = ex;

            while (nestedEx != null)
            {
                if (!string.IsNullOrEmpty(nestedEx.Message))
                {
                    sb.Append(nestedEx.Message + System.Environment.NewLine);
                }

                if (showStackTrace && !string.IsNullOrEmpty(nestedEx.StackTrace))
                {
                    sb.Append(nestedEx.StackTrace + System.Environment.NewLine);
                }

                if (ex is AggregateException)
                {
                    AggregateException ae = ex as AggregateException;

                    foreach (Exception flatEx in ae.Flatten().InnerExceptions)
                    {
                        if (!string.IsNullOrEmpty(flatEx.Message))
                        {
                            sb.Append(flatEx.Message + System.Environment.NewLine);
                        }

                        if (showStackTrace && !string.IsNullOrEmpty(flatEx.StackTrace))
                        {
                            sb.Append(flatEx.StackTrace + System.Environment.NewLine);
                        }
                    }
                }

                nestedEx = nestedEx.InnerException;
            }

            returnValue = sb.ToString();

            return returnValue;
        }
    }
}

........

autofac.Empty.json (set to copy always)

{}

.......

autofac.json (set to copy always)

{
  "defaultAssembly": "MyCompany.MyProject",
  "components": [
    {
      "type": "MyCompany.MyProject.Shippers.FedExShipper",
      "services": [
        {
          "type": "MyCompany.MyProject.Shippers.Interfaces.IShipper"
        }
      ]
    },
    {
      "type": "MyCompany.MyProject.Shippers.UpsShipper",
      "services": [
        {
          "type": "MyCompany.MyProject.Shippers.Interfaces.IShipper"
        }
      ]
    },
    {
      "type": "MyCompany.MyProject.Shippers.UspsShipper",
      "services": [
        {
          "type": "MyCompany.MyProject.Shippers.Interfaces.IShipper"
        }
      ]
    },
    {
      "type": "MyCompany.MyProject.Processors.OrderProcessor",
      "services": [
        {
          "type": "MyCompany.MyProject.Processors.Interfaces.IOrderProcessor"
        }
      ]
    }
  ]
}

and csproj

  
    Exe
    netcoreapp3.1
  

  
    
    
    
    
    
    
    
    
    
    
  

From

https://autofaccn.readthedocs.io/en/latest/integration/netcore.html

PS

In the autofac version I had to change the Logger being injected to be a LoggerFactory.

Here is the OrderProcessor alternate version. You'll have do the same "Microsoft.Extensions.Logging.ILoggerFactory loggerFactory" alternative injection for all 3 concrete "Shipper"'s as well.

namespace MyCompany.MyProject.Processors
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using Microsoft.Extensions.Logging;
    public class OrderProcessor : IOrderProcessor
    {
        ////private readonly IDictionary shippers; /*   :(    I couldn't get IDictionary  to work */
        private readonly IEnumerable shippers;
        private Microsoft.Extensions.Logging.ILogger logger;

        public OrderProcessor(Microsoft.Extensions.Logging.ILoggerFactory loggerFactory, IEnumerable shprs)
        {
            if (null == loggerFactory)
            {
                throw new ArgumentOutOfRangeException("loggerFactory is null");
            }

            if (null == shprs)
            {
                throw new ArgumentOutOfRangeException("ShipperInterface(s) is null");
            }

            this.logger = loggerFactory.CreateLogger();
            this.shippers = shprs;
        }

        public void ProcessOrder(string preferredShipperAbbreviation, Order ord)
        {
            this.logger.LogInformation(string.Format("About to ship. ({0})", preferredShipperAbbreviation));

            /* below foreach is not needed, just "proves" everything was injected */
            int counter = 0;
            foreach (IShipper sh in this.shippers)
            {
                this.logger.LogInformation(string.Format("IEnumerable:ShipperInterface. ({0} of {1}) -> ({2})", ++counter, this.shippers.Count(), sh.GetType().Name));
            }

            IShipper foundShipper = this.FindIShipper(preferredShipperAbbreviation);
            foundShipper.ShipOrder(ord);
        }

        private IShipper FindIShipper(string preferredShipperAbbreviation)
        {
            IShipper foundShipper = this.shippers.FirstOrDefault(s => s.FriendlyNameInstance.Equals(preferredShipperAbbreviation, StringComparison.OrdinalIgnoreCase));

            if (null == foundShipper)
            {
                throw new ArgumentNullException(
                    string.Format("ShipperInterface not found in shipperProviderMap. ('{0}')", preferredShipperAbbreviation));
            }

            return foundShipper;
        }
    }
}

not related to autofac

nlog.config (set to copy always)