Each tutorial or example that I've found for using DI in ASP.NET 5 only shows how it works with Controllers and Razor Views. I need to use DI for other classes but don't know the proper way to resolve types and provide an instance. Right now I have an instance of a HackyDependencyResolver that everything must reference in order to get the proper instances. I want to either access ASP.NET's service resolver or follow some other best-practice for resolving dependencies.
For example if I have
public class SomeClass
{
public SomeClass(IUseMe useMe)
{
}
}
which is not an ASP.NET MVC Controller. I need a pattern for resolving a correct instance for IUseMe when SomeClass is created. Certainly I can make my own global factory, but is that the best way?
DI has nothing to do with asp.net, controllers or views. In the end all are classes. Considering that an action is an entrypoint in your app, any service you need there should be injected, The service itself has some dependencies and those will be injected automatically by the DI Container when it instantiates the controller.
All you have to do is to define your services (not every object needs injected deps) then register those services into the Di Container.
How do I resolve IUseMe so that I'm not dependent on a particular implementation?
You don't. The Di Container does that based on configuration, when the controller is instantiated. Everything has a flow, you don't just pick classes out of thin air and say "I want this created by the Di container". OK you could, but it would be the wrong approach.
The whole point of using a DI Container is not to care about instantiating services. The framework takes care of integrating with the container, your only job is to define the classes properly and to configure the container .
Related
i wanna know if it's possible to inject dependency for a class constructor as it is injected for controllers, i have the following cenario as an example:
An AccountController which depends on an AccountRepository like bellow:
public AccountController(IAccountRepository repository)
The dependency is injected perfectly using Unity DI, which have the following configuration:
container.RegisterType<IUserStore<ApplicationUser>, UserStore<ApplicationUser>>(new HierarchicalLifetimeManager(), accountInjectionConstructor);
container.RegisterType<UserManager<ApplicationUser>>(new HierarchicalLifetimeManager());
container.RegisterType<IdentityDbContext<ApplicationUser>, ApplicationDbContext>(new HierarchicalLifetimeManager());
The problem is that i have a class AuthorizationServiceProvider which also needs the AccountRepository... In this case, how would i instantiate or use this AuthorizationServiceProvider class without having to instantiate and provide it all the dependencies?
Provider = new SimpleAuthorizationServerProvider>(),
This provider is set inside the Startup class and called before the Unity DI config initializes...
Here the visual studio complains that there's no argument given that corresponds to the class constructor, but if i provide a new AccountRepository i'd have to provide all it's dependencies as well, (ApplicationDbContext context, UserManager userManager) which are already provided for the Unity DI when creating the controllers....
Could somebody help me please?
Thanks in advance...
how would i instantiate or use this AuthorizationServiceProvider class without having to instantiate and provide it all the dependencies?
You can't. This is actually the core of what we're trying to achieve with Dependency Injection. Your application code should let go of the control over its dependencies. This means that your application code should not create an AuthorizationServiceProvider. Rather, it should let a third-party provide this dependency. Typically, this means you require the dependency be supplied using Constructor Injection.
Letting application code create these dependencies itself causes problems, typically referred to as the Control Freak anti-pattern or Dependency Inversion Principle violation. It causes strong coupling, which can hinder maintainability.
When working with Dependency Injection, this third-party is called the Composition Root. The Composition Root is:
a (preferably) unique location in an application where modules are composed together.
With DI, only the Composition Root will create graphs of objects. You are using Unity, which is a DI Container. The DI Container acts as the Composer, which is part of your Composition Root.
Instead of using a DI Container, you can build the object graphs by hand, which means you will have to create a complete tree of dependencies at once. This practice is called Pure DI. Still, the Composition Root is the location where those object graphs are created; with or without a DI Container.
Your view of DI might be troubled by the use of the standard Identity template that Visual Studio provides. From a design and DI perspective, however, this template is horrifying.
Either way, all these stated concepts, patterns and anti-patterns are described quite thoroughly in the book Dependency Injection in .NET by Mark Seemann.
I read the article yesterday: https://igor.io/2012/11/09/scaling-silex.html
And another one http://davedevelopment.co.uk/2012/10/03/Silex-Controllers-As-Services.html
So a conceptual question rised in my head:
Currently I do have a lot of controllers in separate classes. I overwrite controller_resolver to create a controller class instance and inject $app into contoller's constructor.
I define routes like this $app->get('/hello', 'HelloController::indexAction') <- my controller resolver will create new HelloController($app); - so far so good.
But to be honest it became a ServiceLocator pattern, not a DependencyInjection, because I do inject whe whole $app which looks like ServiceLocator usage.
Now I am in doubt: should I leave it as is (because it works well) or try "controllers as services" to inject only those sevices on which my controller really depends on? May be my SeviceLocator approach will hit me some day? (people say that DI is better for tests).
I have also looked into Symfony Framework Bundle: class Controller extends abstract class ContainerAware which also have the whole $container injected! ServiceLocator approach in full stack framework?
Any recomendation? Pros/cons?
The symfony2 full-stack framework
The framework uses the Dependency Injection pattern and not the Service Locator pattern.
All controllers aren't services by default. The ContainerAware class includes methods to get access to the service container, so you can call Services inside the Controller.
If you are going to use a Controller as a Service you need to remove the Controller extend. All dependencies you want to use inside the controller needs to be injected by the Service Container.
Read more about this in a blogpost by richard miller, one of the core contributors of Symfony2.
The Silex micro-framework
The Silex micro-framework provides the bare bones of a framework, it's up to you how the architecture looks and which patterns you use.
The Silex documentation uses Controllers that aren't Services. It injects the complete Service Container inside very Controller:
$app->post('/post/{id}-{slug}', function($id, $slug) use ($app) {
// ...
});
If you want to use controllers as service, you should only inject the services you want to use inside the controller.
EDIT: The Controller::action syntax refers also to a Controller that isn't a Service. The Controller:action notation is used to refer to Controllers as Services.
There's lot's of personal preference involved here. What you've done already is a good (enough) step to organising your code base. Some people like myself take things a step further and move our controllers to the container, rather than injecting it in to some kind of BaseController. This happens in both Silex and the full stack Symfony framework.
My advice would be to leave everything you have as is, then try defining your next controller as a service, by practising BDD.
For example, the behaviour of a UserController view action:
It should retrieve the user from a database
It should render the user with a template
Not once does it mention retrieving the database or the template renderer from a container. I'm comfortable not injecting the container, so I'll only inject what I'm led to believe I need by BDD.
When using Unity 2.0 for dependency injection within a web application, it appears that user controls, pages, etc will all need make explicit calls to retrieve the container and "fetch" the dependencies … so using the annotations like [dependency] won't offer any value. This is likely since the location of the container (application context, http context cache, etc.) is unknown in the web configuration.
Since Unity itself provides method interception, isn't there a way to "tell" unity how to fetch the container correctly when you build your own web application? Rather than having to create base classes for page, etc.?
The problem is that the WebForms Pages and Controls are not set up to allow for construction by dependency injection, so Unity never gets invoked at all unless the class invokes Unity itself. I've found the best pattern in these cases is to invoke the DI framework in the constructor via a Service Locator and then use annotations to mark dependency properties. Something like this:
public MyPage()
{
// Injector is a wrapper class so you can change the underlying DI framework
// later if necessary.
Injector.Inject(this);
}
[Dependency]
public SomeService MyService {get;set;}
Whenever I try to actually unit test a presenter and a mocked view, I end up running into too many database dependencies
public EditAccount(IAccountEditPage _view, ISession _session, IResponse _response)
{
}
public void view_SaveUser()
{
//Class that takes the view's data and persists it to DB
}
Obviously I can't write unit tests for this presenter because I have a concretion of using my model class that has a strong database dependency.
How am I supposed to removed the dependency on the database without constructor injecting every class that touches the database in my presenter? I don't want to do this every time in every view I have.
I'm using moq, if it helps.
Edit : Also I should mention that the code in "view_SaveUser" is very lean and isn't direct database access or anything like that. It's usually only a few lines. I'm not overstepping the scope of the presenter, AFAIK.
If you don't want to inject the instances on the constructor another option you have is using a setter injection using a IoC framework as Spring.Net or Castle Windsor to inject the dependencies.
Doing this, you would only need to specify on the framework configuration which classes are used for real code and for test project, dependencies would be automatically injected and you would avoid having to use the contructor.
I'm integrating a series of controllers into an existing project which already contain controllers which use Castle Windsor for DI/IoC. I've modified the Installer to only register Controllers in a certain namespace (specifically the root). This modification appears to be working. When I try to access my controllers, which do not use Castle Windsor and are located in a different namespace (specifically, a custom Area), I get the error message: "No component for supporting the service [Controller Name] was found".
Is it possible to mix "traditional" controllers with controllers which use Castle Windsor in a single project?
Does this make sense?
If you are getting that error, you are trying to resolve the controller (directly or indirectly) through the container.
If you have a separate logic path that needs a controller that isn't register from the container, nothing is stopping you from calling new MyController().
As an aside, thinking in terms of the controller using the container is somewhat backwards. The container manages your instances--your instances have no idea whether they are container-managed or not.