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Injecting dependencies with runtime dependencies

I'm building an application that performs actions initiated by a user and one particular class has dependencies on things I can wire up in DI such as an ILogger instance as well as an HttpClient in addition to runtime arguments that identify the user and the instance of the action (mostly to be used while logging to help with debugging).
The trouble I have is that I'm not entirely sure how to inject this class into the other classes that need it as a result of the runtime dependencies.
Here's a simplified example of one of my classes:
public class Dependency : IDependency
{
private readonly HttpClient httpClient;
private readonly ILogger<Dependency> logger;
private readonly RuntimeDeps runtimeDeps
public Dependency(
ILogger<Dependency> logger,
HttpClient httpClient,
RuntimeDeps runtimeDeps)
{
// set private fields
}
public Result DoStuff()
{
// use Http client to talk to external API
// something fails so log the failure and some helpful info
logger.log($"{runtimeDeps.InstanceId} failed. " +
"Initiated by {runtimeDeps.UserName}");
}
}
This feels like it requires a factory to create but then is it best to request the HttpClient and Logger in the factory method or declare it as a dependency of the factory? If the latter, I presume the factory would have to be registered as a transient or as a scoped resource since registering it as a singleton would result in a captive dependency (I think).
Any suggestions on redesigns are also welcome if this is a symptom of a poor design. I'd love to implement Mark Seeman's Pure DI to get some more assistance from the compiler but I don't know if that's possible in Azure functions.

A transient factory with the transient dependencies injected into the constructor and the runtime dependencies as parameters of the Create method will work fine.
DI is baked into the Azure Functions library in the sense that parameters are injected into the trigger methods, but beyond these you should be able to use Pure DI to manage your own dependencies by calling into some composition root helper class from the trigger function which knows how to build your dependency graph in a pure manner.

Instead of requiring runtime data during the construction of a component, it's better to let runtime data flow through method calls on an initialized object graph by either:
passing runtime data through method calls of the API or
retrieving runtime data from specific abstractions that allow resolving runtime data.
I formalized this in 2015 in this blog post, which I referred to in the comments.
After reading your additional comments, I came to the conclusion that in your case option 2 is most suited, as the data you are sending is likely an implementation detail to the component, and should not be part of the public API.
In that case, you can redesign your component as follows:
public class Dependency : IDependency
{
public Dependency(
ILogger<Dependency> logger,
HttpClient httpClient,
IRuntimeDepsProvider provider) ...
public Result DoStuff()
{
// use Http client to talk to external API
// something fails so log the failure and some helpful info
logger.log($"{provider.InstanceId} failed. " +
$"Initiated by {provider.UserName}");
}
}
IRuntimeDepsProvider is an abstraction that hides the retrieval and storage of runtime data. This gives you the ability to postpone the decision to either use a Closure Composition Model or an Ambient Composition Model until the Last Responsible Moment.
Using the IRuntimeDepsProvider abstraction, you can chose to set the incoming runtime values after the object graph is constructed. For instance:
public class MyFunction
{
// Notice the different abstraction here
public MyFunction(
IRuntimeDepsInitializer initializer,
IHandler<Something> handler) ...
public void TheFunction(Guid instanceId, string userName, Something cmd)
{
// Setting the runtime data *after* the object graph is constructed,
initializer.SetData(instanceId, userName);
// but before the graph's public methods are invoked.
handler.Handle(cmd);
}
}
Here, a second abstraction is introduced, namely IRuntimeDepsInitializer. Now you can have one class implementing both interfaces:
public class RuntimeDepsStorage : IRuntimeDepsInitializer, IRuntimeDepsProvider
{
public Guid InstanceId { get; private set; }
public string UserName { get; private set; }
public void SetData(Guid id, string name)
{
InstanceId = id;
UserName = name;
}
}
TIP: Instead of using two interfaces, you can also use only IRuntimeDepsProvider and let MyFunction depend on the concrete RuntimeDepsStorage. Which solution is best depends on the context.
Now the main trick here is to make sure that RuntimeDepsStorage becomes a Scoped dependency, because you want to reuse it throughout a request, but not shared by multiple requests.
When applying Pure DI, this would look like this:
var storage = new RuntimeDepsStorage();
new MyFuncion(
initializer: storage,
handler: new SomethingHandler(
stuffDoer: new Dependency(
httpClient: client, // Did you notice this is a runtime dep as well?
logger: new Logger<Dependency>(),
provider: storage)))
If, on the other hand, you would be using MS.DI as your DI Container, registration would be similar to the following:
services.AddScoped(_ => new RuntimeDepsStorage());
services.AddScoped<IRuntimeDepsProvider>(
c => c.GetRequiredService<RuntimeDepsStorage>());
services.AddScoped<IRuntimeDepsInitializer>(
c => c.GetRequiredService<RuntimeDepsStorage>());
// etc, your usual registrations here

.NET Core Singleton Creation is called multiple times

I'm registering a service as a singleton in .NET Core. Yet I'm seeing the constructor for the singleton called multiple times.
services.AddSingleton<DbAuthorizationOptions, ContextAuthorizationOptions>();
My context authorization options is just Dictionary of Entity Types to IValidators, The context authorization options are passed into the DBContext, to automatically run validations.
During the registration of my services, I also register dynamic Validators with my container registered in DI.
var useDynamicValidator = serviceOption.ValidatorOptions != null;
if(useDynamicValidator)
{
//TODO: Extract this to before the register service no sense in building the provider each time
//TODO: Make this cleaner don't be dependent on Authorization options
var provider = services.BuildServiceProvider();
var authOptions = provider.GetService<DbAuthorizationOptions>();
var validator = BuildDynamicValidatorFactory(serviceOption).Invoke(provider, null);
authOptions.ValidatorOptions.AddValidatorForSet(validator);
}
I notice that when I call GetService on the provider I receive a new singleton instead of the existing one. Does building the provider create a new container so all of the services get re-registered?
If so, How can I call a method to register my dynamic validators in the singleton container with the existing IServiceProvider, is there a way to invoke some registration once after the service container is built?

Does building the provider create a new container so all of the services get reregistered?
Yes. See the source code.
If so, How can I call a method to register my dynamic validators in the singleton container with the existing IServiceProvider, is there a way to invoke some registration once after the servicecontainer is built?
I'm not really understanding why this is a problem. You should be registering all of your services one time at application startup in the Composition Root.
The DI container is then responsible for resolving the object graphs of the application. The application itself shouldn't have a dependency on it, nor be required to update it.
You should be injecting DbAuthorizationOptions in the place where you need to use it.
public class Foo : IFoo
{
private readonly DbAuthorizationOptions authOptions;
public Foo(DbAuthorizationOptions authOptions) // <-- Inject parameters
{
this.authOptions = authOptions ??
throw new ArgumentNullException(nameof(authOptions));
}
public void DoSomething()
{
// TODO: Inject the type that has the BuildDynamicValidatorFactory
// method and the serviceOption (whatever type that is) here
// either as a method parameter of this method, or a constructor
// parameter of this class.
var validator = BuildDynamicValidatorFactory(serviceOption).Invoke(provider, null);
// Now we have an instance of authOptions that can be used
authOptions.ValidatorOptions.AddValidatorForSet(validator);
}
}
Note that the DI container automatically provides the DbAuthorizationOptions if injected into another type that is also resolved through DI (such as a controller or filter).
NOTE: It isn't very clear from your question where you need to do this. You mention that you want it to happen once, which usually means to put it at application startup. But users cannot interact with code that runs at startup. So, maybe you could use a filter. It really all depends on where in the lifecycle of the application it has to happen.

You can declare a dependency on IServiceProvider -- don't build it, inject it.
public class SomeController
{
DbAuthorizationOptions authOptions;
public SomeController(IServiceProvider provider)
{
authOptions = provider.GetSerivce<DbAuthorizationOptions>();
}
}
But this is the service locator anti-pattern. As I commented on NightOwl888's post after you gave more details, a factory is probably a better approach.

Correctly use Dependency Injection pattern [duplicate]

I'm currently working on a WinForms system (I know) where there's a lot of Constructor Injection when creating forms, but if those forms/views need to open another form, I find the DI container has been injected too so that we can locate the implementation of the desired view interface at runtime. e.g.
public partial class MyView : Form, IMyView
{
private readonly IDIContainer _container;
public MyView(IDIContainer container)
{
InitializeComponent();
_container = container;
}
public OpenDialogClick(object sender, EventArgs e)
{
var dialog = container.Resolve<IDialogView>();
dialog.ShowDialog(this);
}
}
I'm aware that this is basically using the container as a service locator. I've been repeatedly told that this is considered an anti-pattern so I'd like to avoid this usage.
I could probably inject the view as part of the constructor like this :
public partial class MyView : Form, IMyView
{
private readonly IDialogView _dialog;
public MyView(IDialogView dialog)
{
InitializeComponent();
_dialog = dialog;
}
public OpenDialogClick(object sender, EventArgs e)
{
dialog.ShowDialog(this);
}
}
But what if the dialog view is quite expensive to instantiate?
It's been suggested that we create some kind of form factory which internally uses the DI container, but to me this seems like simply creating a wrapper around another service locator.
I know that at some point, something has to know how to create an IDialogView, so I'm thinking that either it's resolved when the composite root is created (probably not ideal if there are many forms and some or all are expensive to create), or the composite root itself has a way to resolve the dependency. In which case the composite root has to have a service-locator-like dependency? But then how would child forms create dialogs like this? Would they call up to the composite via, say, events, to open dialogs like this?
One particular problem I keep running up against is that the container is almost impossible to mock easily. This is partly what keeps me thinking about the form factory idea, even though it would just be a wrapper around the container. Is that a sensible reason?
Have I thought myself into a knot? Is there a simple way through this? Or do I just cut the knot and find something that works for me?

Or do I just cut the knot and find something that works for me?
Factory class:
public interface IDialogFactory {
IDialogView CreateNew();
}
// Implementation
sealed class DialogFactory: IDialogFactory {
public IDialogView CreateNew() {
return new DialogImpl();
}
}
// or singleton...
sealed class SingleDialogFactory: IDialogFactory {
private IDialogView dialog;
public IDialogView CreateNew() {
if (dialog == null) {
dialog = new DialogImpl();
}
return dialog;
}
}
Your code:
public partial class MyView : Form, IMyView {
private readonly IDialogFactory factory;
public MyView(IDialogFactory factory) {
InitializeComponent();
//assert(factory != null);
this.factory = factory;
}
public OpenDialogClick(object sender, EventArgs e) {
using (var dialog = this.factory.CreateNew()) {
dialog.ShowDialog(this);
}
}
}
Registration with SimpleInjector
container.RegisterSingle<IDialogFactory, DialogFactory>();
or using singleton version
container.RegisterSingle<IDialogFactory, SingleDialogFactory>();
container.RegisterSingle<IMyView, MyView>();

A local factory, satisfied with an implementation that uses the container and set up in the composition root is not a service locator, it is a dependency resolver.
The difference is as follows: the locator is defined and satisfied somewhere near the definition of the container. In a separate project, to use the locator, you need an external reference to the container infrastructure. This causes the project to rely on external dependency (the locator).
On the other hand, the dependency resolver is local to the project. It is used to satisfy dependencies in its close neighbourhood but it doesn't depend on anything external.
The composition root should not be used to resolve actual specific dependencies such as the one you are concerned about. Instead, the compositon root should set up implementations of all these local dependency resolvers that are used throughout the application. The more local resolver, the better - the MVC's constructor factory is a good example. On the other hand, WebAPI's resolver handles quite few of different services and it is still a good resolver - it is local in the webapi infrastructure, it doesn't depend on anything (rather - other webapi services depend on it) and it can be implemented in any possible way and set up in the Composition Root.
Some time ago I wrote a blog entry about it
http://www.wiktorzychla.com/2012/12/di-factories-and-composition-root.html
There you will find your issue discussed and an example of how you set up a factory aka resolver.

You definitely do not want to pass your DI container around your application. Your DI container should only be part of your Composition Root. You could, however, have a factory that uses the DI container within the Composition Root. So if Program.cs is where you are wiring everything up, you could simply define that factory class there.
WinForms was not designed with DI in mind; forms are generated and therefore need default constructors. This may or may not be an issue depending on which DI container you use.
I think in this case, the pain of using constructor injection in WinForms is greater than the pain of any pitfalls you may encounter while using a service locator. There's no shame in declaring a static method in your Composition Root (Program.cs) that wraps a call to your DI container to resolve your references.

I know this problem very well. Everything I learned about solution to this (and I learned A LOT) is more or less camouflaging service locator.

Get the container instance for Simple Injector

I am using Simple Injector with a ASP.NET MVC project. I added the SimpleInjector.Integration.Web.Mvc nuget package. This adds SimpleInjectorInitializer class in App_Start folder and initializes the DI. The code looks something like
public static void Initialize()
{
// Did you know the container can diagnose your configuration?
// Go to: https://simpleinjector.org/diagnostics
var container = new Container();
//Container configuration code
DependencyResolver.SetResolver(
new SimpleInjectorDependencyResolver(container));
}
This configures the DI for the MVC controller correctly.
My question is, if I want to get the instance of the container in any of the controller\class to resolve some dependency manually how can I do it.
I have earlier worked on AutoFac and it has a dependency interface IComponentContext which can be injected into any class that needs to do any resolution manually.
Update:
Here is a scenario. My controller uses a service who initialization depends upon the input parameter passed in the controller method and hence the dependency cannot be instantiated during construction time.
I understand that this is somewhat an anti pattern for DI, but it is requirement at few places and hence injecting the DI container is next best thing. Simple Injector samples should use of static variable to share the container which i want to avoid and also it is not possible by the way SimpleInjectorInitializer works.

Except for any code that is part of the startup path of the application, no code should depend directly on the container (or a container abstraction, container facade, etc). This pattern is called Service Locator and Mark Seemann has a good explanation why this is a bad idea.
So components (such as Controllers) should not depend on the container directly, since this hides the used dependencies and makes classes harder to test. Furthermore your code starts to depend on an external framework (making it harder to change) or depending on an abstraction it doesn't need to know about.
My controller uses a service who initialization depends upon the input
parameter passed in the controller method and hence the dependency
cannot be instantiated during construction time
There's a general pattern for this problem: the abstract factory design pattern. The factory pattern allows you to delay the creation of types and allows you to pass in extra runtime parameters for the construction of a certain type. When you do this, your controller doesn't have to depend on Container and it prevents you from having to pass in a constructed container in your unit tests (DI frameworks should in general not be used in your unit test projects).
Do note however that letting your components require runtime data during creation is a code smell. Prevent doing that.
You might think that by doing this we are just moving the problem to the factory implementation. Although we are moving the dependency on the container into the factory implementation, we are in fact solving the problem because the factory implementation will be part of the application's Composition Root, which allows the application code itself oblivious to any DI framework.
So this is how I advice you to structure your code:
// Definition of the factory in the UI or BL layer
public interface ISomeServiceFactory
{
ISomeService Create(int inputParameter);
}
// Controller depending on that factory:
public class MyController : Controller
{
private readonly ISomeServiceFactory factory;
public MyController(ISomeServiceFactory factory)
{
this.factory = factory;
}
public ActionResult Index(int value)
{
// here we use that factory
var service = this.factory.Create(value);
}
}
In your composition root (the start up path) we define the factory implementation and the registration for it:
private class SomeServiceFactory : ISomeServiceFactory
{
private readonly Container container;
// Here we depend on Container, which is fine, since
// we're inside the composition root. The rest of the
// application knows nothing about a DI framework.
public SomeServiceFactory(Container container)
{
this.container = container;
}
public ISomeService Create(int inputParameter)
{
// Do what ever we need to do here. For instance:
if (inputParameter == 0)
return this.container.GetInstance<Service1>();
else
return this.container.GetInstance<Service2>();
}
}
public static void Initialize()
{
var container = new Container();
container.RegisterSingle<ISomeServiceFactory, SomeServiceFactory>();
}
Upon creation, the Container registers itself (using the call RegisterSingle<Container>(this)) so you can always inject the container into any component. That's similar to injecting the IComponentContext when working with Autofac. But the same holds for Autofac, Simple Injector, and any other container: you don't want to inject your container into components that are located outside the composition root (and there hardly ever is a reason for it).

Should creating a Unity Container be considered an expensive operation as it relates to resources and time?

I've recently started using Unity for dependency injections in .net.
I was under the impression that a Unity Container would most likely be a singleton or static member of a class. I saw another developer using it in a request handler that will receive a lot of traffic.
Is there some magic happening that keeps the cost low for creating a new Unity Container every time, or should this code be re-factored to only create the Unity container once?
This code is part of the implementing class of a .svc Service.
public string DoSomeWork(Request request)
{
var container = new UnityContainer().LoadConfiguration("MyContainer");
var handler = container.Resolve<RequestHandler>();
return handler.Handle(request);
}

Not 100% sure with Unity, but with most IoC containers, the creation of the container and especially the loading of container configuration is a reasonably expensive operation.
I have to question why this developer is utilizing the container in this manner however. Ideally the IoC container shouldn't even be a static or singleton object - it should be instantiated only to resolve the top level object of your dependency tree, and the rest of the objects in your application should be constructed automatically through dependency injection. In the case of your example, the class containing that method ideally would have the RequestHandler (ideally an interface of this) injected into it through the constructor so that class does not need to know about the IoC container.

This is not the right way to use an IOC container - basically your are using it as a service locator, but this will cause dependencies to the IOC container to be sprinkled all over the code base.
What you should do is have one central spot in your codebase where all dependencies are resolved and then use dependency injection (DI) to propagate the resolved concrete classes down the chain, i.e via constructor injection. So your class really should look something like this:
public class Foo
{
private readonly IRequestHandler _handler;
public Foo(IRequestHandler handler)
{
_handler = handler;
}
public string DoSomeWork(Request request)
{
return _handler.Handle(request);
}
}