I have an interface for logging the exceptions, i.e. IExceptionLogger.
This interface has 3 implementations: DBExceptionLogger, XMLExceptionLogger, CSVExceptionLogger.
I have an application that will make a use of DBExceptionLogger.
The application references only IExceptionLogger. How do I create an instance of DBExceptionLogger within the application.
I can't reference the DBExceptionLogger directly since it will break the purpose of having IExceptionLogger interface.
You should look at the concepts of inversion of control and dependency injection. These will help you to inject a particular instance of an object that implements your interface, with your code needing to be aware of exactly what it is beyond that fact. There are many libraries to help you in .NET: Unity, Spring.NET, Autofac, LinFu to name but a few.
//Usage of logger with factory
IExceptionLogger logger = ExceptionLoggerFactory.GetLogger();
public static class ExceptionLoggerFactory
{
public static IExceptionLogger GetLogger()
{
//logic to choose between the different exception loggers
//e.g.
if (someCondition)
return new DBExceptionLogger();
//else etc etc
}
}
You can use the Factory pattern (a class whose responsibility is creating an IExceptionLogger class), or more generally, an Inversion of Control framework.
IExceptionLogger logger = new DBExceptionLogger();
then pass logger variable to all your classes which write logging information.
you can use Poor Man's DI with a static factory like this:
public class ExceptionLoggerFactory
{
public static IExceptionLogger GetDBLogger()
{
return new DBExceptionLogger();
}
}
public class MyClass
{
private IExceptionLogger _logger;
public MyClass() : this(ExceptionLoggerFactory.GetDBLogger())
{
}
public MyClass(IExceptionLogger logger)
{
_logger = logger;
}
}
Related
So the way I usually do it (with DI) is to add the extension to my container:
unityContainer.AddNewExtension<Log4NetExtension>();
and then at the constructor of the class where I need to call the logger I use something like this:
public class test
{
private ILog logger;
public test (ILog logger)
{
this.logger =logger;
}
}
Now my problem is, in one of my classes, I don't want to pass anything to the constructor and I was wondering how can I assign my logger (since im using unity I thought of calling resolve but it's not working)
public class test
{
private ILog logger;
public test()
{
logger = unityContainer.Resolve<ILog>(); //I edited this for simplicity
}
}
Error is something like the container didn't know how to resolve ILog.
EDIT:
The class that didn't let me pass anything through its constructor is a Job (implements IJob) class, in the end I ended up using a job listener instead of logging in each job.
Some tips if you still want to pass something for the constructor is by implementation a Job Factory which should help you inject parameters. And I saw a nuget you can add to help you with Quartz integration with Unity.
Log4net allows you create a logger using a name in your class, no need to pass it via a constructor.
Add this as a class member
private static readonly log4net.ILog logger = log4net.LogManager.GetLogger("MyAppLog");
Of course, this does not use your DIContainer.
You can use property injection:
public class test
{
[Dependency]
public ILog Logger { get; set; }
public test()
{
}
}
Two drawbacks, though:
the logger's a public writable property now, so anyone could technically use or overwrite your logger
property injection is meant for optional dependencies, so you might be confusing others who look at the class
I have a class that works with a network via multiple resources. Its constructor receives arguments that are resolved at runtime by IoC container (StructureMap):
public NetworkWorker(IRetryService retryService, ILog log)
{ ... }
What I need is to control the number of resources this class uses on a use-case level - for example, client A need NetworkWorker instance that allows only one operation at a time, while client B need 10 ops at a time.
Currently this number is hardcoded in the constructor. The only way I see is to add a method void Configure(int resourceCount) that each client of NetworkWorker would call with a different value. Or may be there's a better way I don't see?
This class can do different things, but number of resources is required for every method call (Get/Send/etc methods).
P.S. is this a known technique (with a Configure method)? If it is, what's the name for it? smth like 'two-step initialization'?
I'll presume this NetworkWorker has multiple methods (otherwise you could just add a parameter to that single method).
You could use a factory pattern:
public interface INetworkWorkerFactory
{
NetworkWorker Create(int numberOfResources);
}
public class NetworkWorkerFactory : INetworkWorkerFactory
{
private readonly IContainer _container;
public NetworkWorkerFactory(IContainer container)
{
_container = container;
}
public NewtorkWorker Create(int numberOfResources)
{
var retryService = _container.GetInstance<IRetryService>();
var log = _container.GetInstance<ILog>();
return new NewtorkWorker(retryService, log, numberOfResources);
}
}
(or simply inject the required dependencies instead of the container)
and then simply
private readonly INetworkWorkerFactory _networkWorkerFactory;
public C(INetworkWorkerFactory networkWorkerFactory)
{
_networkWorkerFactory = networkWorkerFactory;
}
public void M()
{
var networkWorker = _networkWorkerFactory.Create(10);
}
Autofac uses delegate factories for this.
Other containers have equivalent mechanisms of providing auto-generated Abstract Factories - #ploeh has an awesome SO post aggregating examples.
The code in your question would look like so:
public delegate NetworkWorker Factory(IRetryService retryService);
public NetworkWorker(IRetryService retryService, ILog log)
{ ... }
A consumer would look like so (stolen from Alex's answer)
readonly NetworkWorker.Factory _networkWorkerFactory;
public C(NetworkWorker.Factory networkWorkerFactory)
{
_networkWorkerFactory = networkWorkerFactory;
}
public void M()
{
var networkWorker = _networkWorkerFactory(10);
...
}
The key difference is that you do not declare either an interface or an impl for the Abstract Factory - the delegate is the interface and Autofac 'just knows' to make the rest happen.
Another benefit of this approach (other than the code reduction) is that there's a natural path to transitioning the code to Pure DI)
I have a class (MyFacade) that I injected parameter(s) with Ninject:
class MyFacade
{
IDemoInterface demo;
public MyFacade(IDemoInterface demo)
{
this.demo = demo;
}
public void MyMethod()
{
Console.WriteLine(demo.GetInfo());
}
}
Of course, I have to setup the Ninject to inject the appropiate implementation of my parameter (IDemoInterface)
I know, I can instantiate MyFacade object by doing kernel.Get<MyFacade>(); without setting anything else. Currently my facade doesn't have an interface (because it is my only implementation, maybe I will add its interface for standard proposes)
if I want to make this facade singlenton, I know two ways: create a empty constructor and pass a parameter by doing this kernel.Get<IDemoInterface>(); or by setup Ninject like: kernel.Bind<MyFacade>().To<MyFacade>().InSingletonScope();
The second one look a better approach, but do you know any other way to setup it in a singleton way?
When setting up your bindings, you need to bind your dependencies. It is always better to setup your dependencies in your bindings, as opposed to doing a kernel.Get<T>() in a constructor. You are using IOC, so leverage the framework you are using to do the injection for you.
In your second example binding, what you are missing is binding in your IDemoInterface. Your bindings should look like this:
//bind the dependency to the implementation.
kernel.Bind<IDemoInterface>().To<DemoInterface>();
//since you bound your dependency, ninject should now have
// all the dependencies required to instantiate your `MyFacade` object.
kernel.Bind<MyFacade>().To<MyFacade>().InSingletonScope();
If you do not want the container to manage the lifecycle of your singleton by using InSingletonScope(), but still wants it to get injected, I can think of 2 ways to go about it. Choose which one suits better to your needs. Consider the following ISingleton (name your interface) implementation:
public class ConcreteSingleton : ISingleton
{
private static readonly Lazy<ConcreteSingleton> _instance = new Lazy<ConcreteSingleton>(() => new ConcreteSingleton());
private ConcreteSingleton() { }
public static ConcreteSingleton Instance
{
get
{
return _instance.Value;
}
}
}
Alter the singleton class to have a GetInstance(...) method
In this method (my preferred approach), you won't be calling kernel.Inject(instance) each time, only for the first time the singleton is initialized. Adding the following method to your ConcreteSingleton class:
public static ConcreteSingleton GetInstance(IKernel kernelForInjection)
{
if (_instance.IsValueCreated == false)
{
kernelForInjection.Inject(_instance.Value);
}
return _instance.Value;
}
And using this binding:
kernel.Bind<ISingleton>().ToMethod(c => ConcreteSingleton.GetInstance(c.Kernel));
Will achieve the desired behavior of not having a public constructor but enabling your facade to be efficiently injected.
Perform injection each time the ISingleton instance is requested
If by any reason you are not allowed to modify your ConcreteSingleton: This approach will wrap the singleton creation in a provider to efficiently inject the instance only for the first time it is created. It is important to note that the provider itself must be registered as a singleton.
internal class ConcreteSingletonProvider : Provider<ISingleton>
{
public IKernel Kernel { get; set; }
//Just a wrapper
private readonly Lazy<ISingleton> _lazy = new Lazy<ISingleton>(() => ConcreteSingleton.Instance);
public ConcreteSingletonProvider(IKernel kernel)
{
Kernel = kernel;
}
protected override ISingleton CreateInstance(IContext context)
{
if (_lazy.IsValueCreated == false)
{
Kernel.Inject(ConcreteSingleton.Instance);
}
return _lazy.Value;
}
}
And your bindings should be like this:
kernel.Bind<ISingleton>().ToProvider<ConcreteSingletonProvider>();
kernel.Bind<ConcreteSingletonProvider>().ToSelf().InSingletonScope();
This gist has a complete working sample for the above approach.
Hope that helps!
I have the IRespository registered twice (with names) in the following code:
// Setup the Client Repository
IOC.Container.RegisterType<ClientEntities>(new InjectionConstructor());
IOC.Container.RegisterType<IRepository, GenericRepository>
("Client", new InjectionConstructor(typeof(ClientEntities)));
// Setup the Customer Repository
IOC.Container.RegisterType<CustomerEntities>(new InjectionConstructor());
IOC.Container.RegisterType<IRepository, GenericRepository>
("Customer", new InjectionConstructor(typeof(CustomerEntities)));
IOC.Container.RegisterType<IClientModel, ClientModel>();
IOC.Container.RegisterType<ICustomerModel, CustomerModel>();
But then when I want to resolve this (to use the IRepository) I have to do a manual resolve like this:
public ClientModel(IUnityContainer container)
{
this.dataAccess = container.Resolve<IRepository>(Client);
.....
}
What I would like to do is to have it resolved in the constructor (just like IUnityContainer). I need some way to say which named type to resolve to.
Something like this: (NOTE: Not real code)
public ClientModel([NamedDependancy("Client")] IRepository dataAccess)
{
this.dataAccess = dataAccess;
.....
}
Is there a way to make my fake code work?
You can configure dependencies with or without names in the API, attributes, or via the config file. You didn't mention XML above, so I'll assume you're using the API.
To tell the container to resolve a named dependency, you'll need to use an InjectionParameter object. For your ClientModel example, do this:
container.RegisterType<IClientModel, ClientModel>(
new InjectionConstructor( // Explicitly specify a constructor
new ResolvedParameter<IRepository>("Client") // Resolve parameter of type IRepository using name "Client"
)
);
This tells the container "When resolving ClientModel, call the constructor that takes a single IRepository parameter. When resolving that parameter, resolve with the name 'Client' in addition to the type."
If you wanted to use attributes, your example almost works, you just need to change the attribute name:
public ClientModel([Dependency("Client")] IRepository dataAccess)
{
this.dataAccess = dataAccess;
.....
}
This is a very late response but the question still shows up in Google.
So anyways, 5 years later...
I have a pretty simple approach. Usually when you need to use "named dependency" it's because you're trying to implement some kind of strategy pattern. In that case, I simply create a level of indirection between Unity and the rest of my code called the StrategyResolver to not be directly depending on Unity.
public class StrategyResolver : IStrategyResolver
{
private IUnityContainer container;
public StrategyResolver(IUnityContainer unityContainer)
{
this.container = unityContainer;
}
public T Resolve<T>(string namedStrategy)
{
return this.container.Resolve<T>(namedStrategy);
}
}
Usage:
public class SomeClass: ISomeInterface
{
private IStrategyResolver strategyResolver;
public SomeClass(IStrategyResolver stratResolver)
{
this.strategyResolver = stratResolver;
}
public void Process(SomeDto dto)
{
IActionHandler actionHanlder = this.strategyResolver.Resolve<IActionHandler>(dto.SomeProperty);
actionHanlder.Handle(dto);
}
}
Registration:
container.RegisterType<IActionHandler, ActionOne>("One");
container.RegisterType<IActionHandler, ActionTwo>("Two");
container.RegisterType<IStrategyResolver, StrategyResolver>();
container.RegisterType<ISomeInterface, SomeClass>();
Now, the nice thing about this is that I will never have to touch the StrategyResolver ever again when adding new strategies in the future.
It's very simple. Very clean and I kept the dependency on Unity to a strict minimum. The only time I would have touch the StrategyResolver is if I decide to change container technology which is very unlikely to happen.
Hope this helps!
Edit: I don't really like the accepted answer because when you use the Dependency attribute in your service's constructor you actually have a hard dependency on Unity. The Dependency attribute is part of the Unity library. At that point you might as well pass an IUnityContainer dependency everywhere.
I prefer having my service classes depend on objects that I completely own instead of having a hard dependency on an external library all over the place. Also using Dependency attribute makes the constructors signatures less clean and simple.
Furthermore, this technique allows to resolve named dependencies at runtime without having to hardcode the named dependencies in the constructor, in the application configuration file or use InjectionParameter which are all methods that require to know what named dependency to use at design time.
Edit (2016-09-19):
For those that might wonder, the container will know to pass itself when you are requesting IUnityContainer as dependency, as shown in the StrategyResolver constructor signature.
Edit (2018-10-20):
Here's another way, simply using a factory:
public class SomeStrategyFactory : ISomeStrategyFactory
{
private IStrategy _stratA;
private IStrategy _stratB;
public SomeFactory(IStrategyA stratA, IStrategyB stratB)
{
_stratA = stratA;
_stratB = stratB;
}
public IStrategy GetStrategy(string namedStrategy){
if (namedStrategy == "A") return _stratA;
if (namedStrategy == "B") return _stratB;
}
}
public interface IStrategy {
void Execute();
}
public interface IStrategyA : IStrategy {}
public interface IStrategyB : IStrategy {}
public class StrategyA : IStrategyA {
public void Execute(){}
}
public class StrategyB : IStrategyB {
public void Execute() {}
}
Usage:
public class SomeClass : ISomeClass
{
public SomeClass(ISomeStrategyFactory strategyFactory){
IStrategy strat = strategyFactory.GetStrategy("HelloStrategy");
strat.Execute();
}
}
Registration:
container.RegisterType<ISomeStrategyFactory, SomeStrategyFactory>();
container.RegisterType<IStrategyA, StrategyA>();
container.RegisterType<IStrategyB, StrategyB>();
container.RegisterType<ISomeClass, SomeClass>();
This 2nd suggestion is the same thing but using the factory design pattern.
Hope this helps!
You should be able to use ParameterOverrides
var repository = IOC.Container.Resolve<IRepository>("Client");
var clientModel = IOC.Container.Resolve<ClientModel>(new ParameterOverrides<ClientModel> { {"dataAccess", repository } } );
edit:
I'm not sure why you're passing around the UnityContainer - personally, we inject our dependencies into the constructor themselves (which is "normal" from what I've seen). But regardless, you can specify a name in your RegisterType and Resolve methods.
IOC.Container.RegisterType<IRepository, GenericRepository>("Client");
IOC.Container.Resolve<IRepository>("Client");
and it will give you the type you registered for that name.
Don't do this - just create a class ClientRepository : GenericRepository { } and utilise the Type system.
A quick description of the environment:
I have a class that represents a chatroom and has a dependency on a logger. It's not the same as a system-wide logger with cross-cutting concerns, but a logger that's tied to that specific chatroom. It logs all activity in that chatroom to it's unique log file. When the chatroom is created I want to open the log file, and when it's destroyed I want to close the log file.
The Problem
Here's the relevant code I'm using.
public interface IChatroomLogger
{
void Log(ServerPacket packet);
void Open();
void Close();
}
public class ChatroomLogger : IChatroomLogger
{
// chatroom name will be used as a file name
public ChatroomLogger(string chatroomName) { ... }
public void Log(ServerPacket packet) { ... }
}
public class Chatroom
{
public Chatroom(string name, IChatroomLogger logger)
{
this.name = name;
this.logger = logger;
this.logger.Open();
}
public IChatromLogger Logger { get { return this.logger; } }
}
public interface IChatManager
{
Chatroom Get(chatroomName);
}
It's used in the application like this:
var room = ChatManager.Get(chatroomName);
romm.DoStuff();
room.Logger.LogPacket(receivedPacket);
The ChatManager is a class which holds references to all chatrooms and is responsible for creating and removing them. I haven't written it yet but that's the interface I've been coding against.
The Question
How do I get ChatManager to create new instances of Chatroom and still use dependency injection??
I'm using Unity to do all my other DI stuff. So far it's worked great. But I'm not sure how to work around this conundrum.
When my concrete implementation of ChatManager creates new chatrooms, it has to pass in an IChatroomLogger. It doesn't know how to construct that...but Unity does. But then I have to pass in IUnityContainer into the ChatManager.
public class ChatManager : IChatManager
{
public ChatManager(IUnityContainer container)
{
this.container = container;
}
public Chat Get(string chatroomName)
{
// get logger from Unity somehow. Not sure how I'd
// pass chatroomName to the concrete instance
var logger = ...
return new Chatroom(chatroomName, logger);
}
}
That just seems wrong for some reason. It seems cleaner to not have the domain know anything about what DI container I'm using.
How could I get new instances of class Chatroom while my application in the middle of running without resorting to some sort of service locator design? Am I overthinking it? Is it not a big deal to pass around Unity? Any thoughts are welcome!
You're right. Using the IUnityContainer like this is no longer using Dependency Injection. Instead it's using the "Service Locator" pattern. What I usually do in cases like this is create an IFactory<T> interface, like this:
public IFactory<T>
{
T Get();
}
Then implement the interface with a class that does know about and use the IUnityContainer. Set up your bindings so that IFactory<> requests will create an instance of this factory class. That way, you can inject the IFactory<Logger> interface into your ChatManager, and call .Get() any time you want a logger instance.
In general, I also think you should avoid passing the container around.
Add a IChatroomProvider to your design with a Create(string roomname) method
In ChatroomProvider, use the container to create named instances (the container will manage the lifecyle of each named instance for you so you don't need to manage a dictionary).
Register the ChatroomProvider with the container
Let ChatManager take a dependency on IChatroomProvider
When ChatManager needs a chatroom it can just ask its IChatroomProvider
Use the container to create the ChatManager instance
Logger instances will be created when chatrooms are created