Lets say that I have two services that depend on one interface:
class Service1
{
...
Service1(IDependency dependency) { ... }
...
}
and
class Service2
{
...
Service2(IDependency dependency) { ... }
...
}
IDependency is registered by some concrete implementation. How can I register decorator to IDependency implementation that can be consumed only by Service2? In other words IDependency should be resolved to an instance of the decorator only inside Service2. Is it possible?
You can use context-based injection
// Register decorators first
container.RegisterConditional<IDependency, DependencyDecorator1>(
c => c.Consumer.ImplementationType == typeof(Service1));
container.RegisterConditional<IDependency, DependencyDecorator2>(
c => c.Consumer.ImplementationType == typeof(Service2));
// Register the real implementation last using !c.Handled
container.RegisterConditional<IDependency, RealImplementationDependency>(
c => !c.Handled);
See the note from the documentation:
Note: In many cases context based injection is not the best solution,
and the design should be reevaluated. In some narrow cases however it
can make sense.
Alternatively, you could derive separate interfaces that extend IDependency and use those, one for each service. This might be more appropriate to differentiate the dependencies. In this case, you'd simply register different implementation/instances for each interface.
For example, you might have a file storage abstraction against a cloud storage service. The basic interface encapsulates all the file storage actions, then you extend it for specific buckets within the storage container. You can provide a single implementation (via delegate registration) that takes the storage bucket as a constructor parameter for each named interface. The use of named interfaces that identify the bucket purpose enhance code comprehension.
public interface IFileStorage
{
...
}
public interface IUploadStorage : IFileStorage { /* empty interface */ }
public interface IContentStorage : IFileStorage { /* empty interface */ }
public class FileStorage : IUploadStorage, IContentStorage
{
public FileStorage(string containerName) { ... }
...
}
public UploadService(IUploadStorage storage)
{
...
}
public ContentService(IContentStorage storage)
{
...
}
container.Register<IUploadStorage>(() = new FileStorage(Containers.Upload));
container.Register<IContentStorage>(() = new FileStorage(Containers.Content));
Related
In my startup.cs I have code like this
services.AddScoped<IFileStorage, DiskFileStorage>();
service.Add<IImageHandler, ImageHandler>();
public class ImageHandler
{
ImageHandler(IFileStorage fileStorage, ...){}
}
now I want to add another class, OtherHandler, that takes a IFileStorage interface, but with another implementation, something like this
services.AddScoped<IFileStorage, NetworkFileStorage>();
public class OtherHandler:IOtherHandler
{
OtherHandler(IFileStorage, fileStorage)
}
Now how do i configure stuff so that the OtherHandler would use the NetworkFileStorage implementation for IFileStorage and anything else would use a default DiskFileStorage implementation?
Update:
Thanks to gunr2171 comment, I discovered that I could do a
services.AddScoped<IOtherHandler>(provider => new OtherHandler(provider.GetRequiredService<NetworkFileStorage>())); to get a specific implementation. But still curious if it is possible if I for some reason wanted to use an interface.
So, based on my understanding this is your scenario:
public interface IFileStorage
{
}
public class NetworkFileStorage: IFileStorage
{
}
public class DiskFileStorage: IFileStorage
{
}
You also have a couple of services depending on the IFileStorage service:
public class ImageHandler: IImageHandler
{
public ImageHandler(IFileStorage fileStorage)
{
}
}
public class OtherHandler: IOtherHandler
{
public OtherHandler(IFileStorage fileStorage)
{
}
}
You want to register your services so that both of the followings hold true:
instances of ImageHandler are built by injecting NetworkFileStorage
instances of OtherHandler are built by injecting DiskFileStorage
For simplicity, I'll suppose that all the involved types are implemented so that it is ok to register them as singletons. This depends on the actual implementation, in any case the pattern that I'm going to show you doesn't depend on the actual lifetime of the involved types.
First of all, register the concrete implementations of the IFileStorage interface. You need to register the classes (not the interface): the purpose of this is making sure that the DI container knows these types and it is able to provide you instances of both types.
services.AddSingleton<NetworkFileStorage>();
services.AddSingleton<DiskFileStorage>();
Now, you can register an implementation for the IImageHandler service.
You will use the ImageHandler class as the implementing type and you will also provide a factory method to the DI container: by doing so, you are able to select the implementation of IFileStorage to be injected (in this case you will select the NetworkFileStorage type).
services.AddSingleton<IImageHandler>(sp =>
{
var fileStorage = sp.GetRequiredService<NetworkFileStorage>();
return ActivatorUtilities.CreateInstance<ImageHandler>(sp, fileStorage);
});
You can do a similar thing to register the OtherHandler class as the implementation for the IOtherHandler service, and select the class DiskFileStorage as the type being injected in the constructor of OtherHandler:
services.AddSingleton<IOtherHandler>(sp =>
{
var fileStorage = sp.GetRequiredService<DiskFileStorage>();
return ActivatorUtilities.CreateInstance<OtherHandler>(sp, fileStorage);
});
Let me add a final note on your design. There is something wrong with it.
It seems to me that the ImageHandler class is somewhat strongly coupled with the NetworkFileStorage class, while the OtherHandler class is somewhat strongly coupled with the DiskFileStorage class.
I would expect both of these classes to work fine with any implementation of the IFileStorage interface. If these classes do really depend only on the behavior described by the IFileStorage interface, then any actual implementation of that behavior should be fine for them to work as expected. This is basically a violation of the Liskov Substitution Principle.
If this is not the case, maybe the interface IFileStorage is not a useful abstraction for your domain model and you should considered to redesign it or to define two different interfaces (one suited to the needs of the ImageHandler class and the other suited to the needs of the OtherHandler class).
I think there might be a more flexible approach here. It uses Adapter pattern for your services, allowing you to stay away from registering concrete implementations, and doesn't force you to instantiate every type manually that uses some FileStorage implementation.
// A generic storage that can be used for any scenario
public interface IFileStorage<T> where T : IFileAdapter
{
protected T Adapter { get; }
Task Handle();
}
// a base interface that defines the shape of adapter
public interface IFileAdapter
{
Task Handle();
}
// copy interfaces to separate the services
public interface ILocalFileAdapter : IFileAdapter
{
}
public interface IRemoteFileAdapter : IFileAdapter
{
}
// specific implementations
public class RemoteFileAdapter : IRemoteFileAdapter
{
private readonly ILogger<RemoteFileAdapter> logger;
public RemoteFileAdapter(ILogger<RemoteFileAdapter> logger)
{
this.logger = logger;
}
public Task Handle()
{
this.logger.LogWarning("Handling file remotely");
return Task.CompletedTask;
}
}
public class LocalFileAdapter : ILocalFileAdapter
{
private readonly ILogger<LocalFileAdapter> logger;
public LocalFileAdapter(ILogger<LocalFileAdapter> logger)
{
this.logger = logger;
}
public Task Handle()
{
this.logger.LogWarning("Handling file locally");
return Task.CompletedTask;
}
}
// generic storage that uses an adapter to handle the scenario
public class FileStorage<T> : IFileStorage<T> where T : IFileAdapter
{
public FileStorage(T fileAdapter)
{
Adapter = fileAdapter;
}
public T Adapter { get; }
public Task Handle()
{
return this.Adapter.Handle();
}
}
Register your services like below :
builder.Services.AddSingleton<ILocalFileAdapter, LocalFileAdapter>();
builder.Services.AddSingleton<IRemoteFileAdapter, RemoteFileAdapter>();
// aspnet.core allows you to register generic services
builder.Services.AddSingleton(typeof(IFileStorage<>), typeof(FileStorage<>));
And this is how you use your IFileStorageService:
public WeatherForecastController(IFileStorage<ILocalFileAdapter> localFileStorage, IFileStorage<IRemoteFileAdapter> remoteFileStorage)
{
localFileStorage.Handle();
remoteFileStorage.Handle();
}
// which will log :
// Handling file locally
// Handling file remotely
I'm getting myself tied in knots with generics and after some advice. Say I have the following interface:
public interface IThing<T>
{
string DoStuff(T input);
}
and the following implementations:
public class GenericThing<T> : IThing<T> where T : Person
{
public string DoStuff(T input)
{
return typeof(T).Name;
}
}
and
public class GenericThing2<T> : IThing<T> where T : Animal
{
public string DoStuff(T input)
{
return typeof(T).Name;
}
}
Registered as follows:
services.AddSingleton(typeof(IThing<>), typeof(GenericThing<>));
services.AddSingleton(typeof(IThing<>), typeof(GenericThing2<>));
Is there a way of identifying all objects that implement IThing<> in the services collection?
You could iterate over the Service Descriptors in the ServiceCollection and examine the types to see which ones are generic and what the generic type parameters are.
Generally I would recommend registering concrete types in the service provider rather than abstract ones, because it will be difficult to create a service that does not have a concrete type! For example,
services.AddSingleton( typeof(IThing<Person>, GenericThing<Person>)
You also may want to provide a name string for the service in cases where you want to register the same interface you're twice, because otherwise there is no way to distinguish between the multiple services when you try to Get Service. Usually however one tries to avoid registering the same interface twice.
sjb
I have two implementations of a generic interface.
public class ConcreteComponent1<T>:IService<T>{}
public class ConcreteComponent2<T>:IService<T>{}
I have a factory which will create the proper concrete implementation.
public class ServiceFactory
{
public IService<T> CreateService<T>()
{
//choose the right concrete component and create it
}
}
I have a registered the below service consumer which will consume the service.
public class Consumer
{
public Consumer(IService<Token> token){}
}
I am not sure how to register a provider for open generic service with autofac. Any help appreciated. Thanks in advance.
As #Steven said I would also recommend against using a factory. Instead you could register your IService<T> as named or keyed service and then decide in the constructor of the Consumer class which implementation you want to use:
containerBuilder.RegisterGeneric(typeof(ConcreteComponent1<>)).Named("ConcreteComponent1", typeof(IService<>));
containerBuilder.RegisterGeneric(typeof(ConcreteComponent2<>)).Named("ConcreteComponent2", typeof(IService<>));
containerBuilder.RegisterType<Consumer>();
Then you can use the IIndex<K,V> class to get all the named implementations of your IService<T> class:
public class Consumer
{
private readonly IService<Token> _token;
public Consumer(IIndex<string, IService<Token>> tokenServices)
{
// select the correct service
_token = tokenServices["ConcreteComponent1"];
}
}
Alternatively if you don't want to name your services you can also get all available implementations by injecting IEnumerable<IService<Token>> and then choose the correct service however you like.
I have the following problem. I have one interface say IFoo and multiple implementations from it. Now, I have one web API controller, which according to some circumstances, should create a particular type of IFoo descendant, call it's method(s) and return result. The logic of the controller doesn't change no matter which implementation of IFoo I use. For this task, I need to tell the container which IFoo implementation to create from the controller, the problem is that, I don't know how to do that (if it's even possible with Simple Injector).
P.S. I already thought about RegisterAll, but in this case I'm forced to create all IFoo descendants (and pass it to the controller) when I need only one. This is not a solution for me.
Another solution would be to create different controllers for different IFoo implementations and use context based injection, but this will result in duplicated code/controllers that I want to avoid.
Ideally, the solution should be something like
container.RegisterAllWithMetadata(IEnumerable<Type> types, IEnumerable<string> metadata)
container.GetInstance(Type type, string metadata)
Is it possible to achieve my goal with Simple Injector?
sorry for bringing it back to life, but as it was said in the comments by Steven, your answer is in the docs
In situations where a service needs to create multiple instances of a certain dependencies, or needs to explicitly control the lifetime of such dependency, abstract factories can be used. Instead of injecting an IMyService, you should inject an IMyServiceFactory that creates new instances of IMyService:
// Definition
public interface IMyServiceFactory {
IMyService CreateNew();
}
// Implementation
sealed class ServiceFactory : IMyServiceFactory {
public IMyService CreateNew() {
return new MyServiceImpl();
}
}
// Registration
container.RegisterSingle<IMyServiceFactory, ServiceFactory>();
// Usage
public class MyService {
private readonly IMyServiceFactory factory;
public MyService(IMyServiceFactory factory) {
this.factory = factory;
}
public void SomeOperation() {
using (var service1 = this.factory.CreateNew()) {
// use service 1
}
using (var service2 = this.factory.CreateNew()) {
// use service 2
}
}
}
Let's say in C# I have a class called A
public class A : IInterfaceA
{
[Dependency]
B _b;
}
Then in B class I have a constructor like this:
public class B
{
...
public B(string someParam) { ... }
...
}
Now, I register class A like this:
_unityContainer.RegisterType<IInterfaceA, A>("RegistrationA");
and to resolve the interface I do:
_unityContainer.Resolve<IInterfaceA>("RegistrationA", new ParameterOverride("someParam", "The param."));
Now I want to know if it is good practice to resolve the class and pass the parameters like this or I should do it another way.
Thanks a lot :)
First of all the code you posted does not work: in fact you're overriding the parameter of class A, while in your code the constructor with the parameter is B.
Generally speaking, using parameter override is not a good practice in my opinion (unless some very specifical context like a console application or a web service using an existing container but it's avoidable in most cases) for these reason:
Using Resolve looks like a Service locator: anti-pattern nowadays. You will find a lot of discussion googling about.
Using ParameterOverride means that the client (the caller of Resolve) knows exactly the type mapped in the container and wants that type initialized with a specific parameter. But this is just the opposite of inversion of control.
The best way is to use an abstract factory. You can add in your code and use a more flexible and SOLID abstract factory:
public interface BFactory {
B Create(string bparam);
}
public class BFactoryUnity : BFactory {
private IUnityContainer container;
public BFactoryUnity(IUnityContainer container) {
this.container = container;
}
public B Create(String bParam) {
var b = new B(bParam);
container.BuildUp(b);
return b;
}
}
So you can register:
_unityContainer.RegisterType<IInterfaceA, A>("RegistrationA")
.RegisterType<BFactory, BFactoryUnity>();
Now the client can resolve only the factory and use it:
var bFactory = _container.Resolve<BFactory>();
var b = bFactory.Create();
Now, in a big application you will need a lot of similar factories. To avoid the boilerplate code of abstract factories and implementations you can find in the web some implementation of automatic abstract factory extensions.