I have a class which needs to use an IRepository for one method in it's class.
Ideally, I would like to avoid having to resolve this dependency into the class's constructor, and so I found method level injection in Ninject and was wondering how this works?
I understand how to set it up. What I'm confused about is how to call it?
Example:
class SomeClassThatUsesRepository
{
[Inject]
public void QueryForSomeStuff(IRepository repository)
{
//do some stuff
}
}
My problem is how do I call this method without specifying an IRepository?
var someClass = Kernel.Resolve<SomeClassThatUsesRepository>();
would work if I was using the constructor, but I want to call a method.
How do I call a method using Ninject method injection?
I'm afraid method injection doesn't work this way - it's just one of the ways to inject dependencies into an object during its construction (you can inject your dependencies through constructor parameters, through properties, fields or methods). Method injection is useful if your class takes its dependencies by Java-style setter methods like
public void SetRepository(IRepository repository) { ... }
If it is marked with [Inject] attribute, you don't need to call this methods directly, it is to be called by Ninject during the initialization to pass the IRepository object into your resolved object.
So I believe your QueryForSomeStuff method is being called when you resove your SomeClassThatUsesRepository.
Confirmed that method injection doesn't work as intended. Got a custom MVC attribute class and wanted to use an injected object inside it. Did not pass it
into the constructor and added method
[Ninject.Inject]
public void ResolveDI(ISettingStore store)
{
ConfigHelper = store;
}
This method was never called and ConfigHelper was null when the attribute's OnActionExecuting was called.
Related
I'd like to write a little stub for a service class. The reason is, that I don't want to push the secret API keys that the service class needs to the CI and I don't want the service class in the CI to run against the external service anyways.
However, the service class is non-abstract and has a private constructor.
When I try to create my stub class like:
open class FirebaseMock: FirebaseMessaging {
// implemented functions go here
}
it says
This type has a constructor, and thus must be initialized here
If I try to initialize it like:
open class FirebaseMock: FirebaseMessaging() {
// implemented functions go here
}
it goes
Cannot access '<init>': it is private in 'FirebaseMessaging'
Which is true:
private FirebaseMessaging(Builder builder) {
...
All I want to do is make my stub class formally a subclass of FirebaseMessaging to use it as placeholder, that mocks the FirebaseMessaging-Functionality when the API keys are not present.
How can I just implement a non-abstract, non-interface class, that has a private constructor nonetheless.
My current solution is a wrapper, which works but is not as nice.
Mockito etc. does not seem like a good solution, since this is still in the productive code.
I want to send message from Service A using SignalR when some event occures (for example, message from Service B received).
So hub method needs to be called from some sort of handler, that not constructed using Dependency Injection. How I can do this?
So far, I tried and read about the following things:
I can inject context into Controller and lead it to my handler. I probably can do that, but passing hub context from the top (controller class) to the bottom (handler class) is not the best approach, which adds a lot of dependencies to the classes that should not be aware of this context, so I would like to avoid that.
I can inject my IHubContext in "any" class, but then, the thing is, how to get an instance of that class on my handler?
Add Static method to class with injected context!? Well, that works until you have 1 client because with new client static property is going to be overwritten.
So I cannot imagine, how handler can use dependency injected IHubContext.
Probably, someone did that before and have an example of how to truly inject context into any class.
Thank you in advance and any additional information will be provided, if necessary.
Answer 1
Here is one possible solution. Implement a factory pattern. Create a factory that knows how to create your handler. Inject the IHubContext in the factory. You can use a few approaches that way:
Construct the Handler by passing in the IHubContext
Create a public property in the Handler and set the IHubContext
Create a method in the Handler and pass the IHubContext as a parameter
You can decide whichever approach suits you. Inject that factory in the controller via DI, and get the handler using the factory method. That way you are not exposing the IHubContext. Please see the code below
public interface IHandlerFactory
{
Handler CreateHandler();
}
public class HandlerFactory : IHandlerFactory
{
private IHubContext _hubContext;
public HandlerFactory(IHubContext context)
{
_hubContext = context;
}
public Handler CreateHandler()
{
return new Handler(param1, param2, _context);
}
}
Then in the entry point, controller/service, inject the factory via DI
public class MyController : Controller
{
private Handler _handler;
public MyController(IHandlerFactory factory)
{
_handler = factory.CreateHandler();
}
}
Then you can use that _handler in the other methods. I hope this helps.
Answer 2
Another possible solution is to use IHostedService if it's possible at all for you. Please see a solution to a GitHub issue, provided by David Fowler here, that I think somewhat relevant to your scenario.
In Autofac we have PropertiesAutoWired. Its written there
If the component is a reflection component, use the PropertiesAutowired() modifier to inject properties.
Appears that we should use this when we need to do property injection. So I want to know what would it be in case of Ninject.
Ninject doesn't feature an equivalent to Autofacs PropertiesAutowired(). Instead one marks properties with an attribute [Inject] - the binding of the component is unaffected:
public class FooBar
{
// will be injected
[Inject]
public IDependency Dependency { get; set; }
// will not be injected
public IFalaffel Falaffel {get; set;
}
The binding is not affected. For example
Bind<FooBar>().ToSelf();
is perfectly valid and (attributed) properties will be injected.
Also see the Property Injection documentation on the ninject wiki.
Furthermore note, that constructor injection is the preferred alternative. You should only use property injection in case you can't use constructor injection or some other special circumstances, like you cannot get rid of an inheritance hierarchy and don't want to pass constructor parameters down 10 steps in a class hierarchy...
Alternative to using Attributes
If you don't want to clutter your code with references to Ninject, you can also do property injection like this:
Bind<FooBar>().ToSelf()
.OnActivation((ctx, instance) => instance.Dependency = ctx.Kernel.Get<IDependency>());
I am using the following Ninject related nuget packages in an MVC 5 WebAPI application:
Ninject.MVC5
Ninject.Extensions.Factory
ninject.extensions.conventions
I have a simple repository and a corresponding factory class like so:
public interface ITaskRunner
{
void Run();
}
public interface IRepository<T> where T: class
{
T[] GetAll();
}
public interface IRepositoryFactory<T> where T: class
{
IRepository<T> CreateRepository();
}
I have setup the Ninject bindings using ToFactory() from Ninject.Extensions.Factory like so:
kernel.Bind<ITaskRunner>().To<TaskRunner>().InSingletonScope();
kernel.Bind(typeof(IRepository<>)).To(typeof(Repository<>)).InRequestScope();
kernel.Bind<IRepositoryFactory<Contact>>().ToFactory();
I am using the factory in the following class:
public class TaskRunner : ITaskRunner
{
//MyTask is a simple POCO class(not shown for brevity)
IRepositoryFactory<MyTask> repoFactory = null;
IRepository<MyTask> repo = null;
public TaskRunner(IRepositoryFactory<MyTask> repoFactory)
{
this.repoFactory = repoFactory;
repo = repoFactory.CreateRepository();
}
//implementation elided
}
I am noticing that the call to repoFactory.CreateRepository() always returns the same instance of the factory (dynamic proxy) that Ninject generates.
Question : Is there a way to change/control this behavior and set a "lifetime" such as Transient, PerThread etc. for the instance that "CreateRepository" returns?
In this particular case, tasks might be processed asynchronously on multiple threads and the repository is not thread safe and hence singleton behavior for the instance returned from "CreateRepository" is not desirable.
I'm not sure what you are trying to achieve, but results you are seeing are quite expected because your TaskRunner is bound as Singleton (so constructed once), and you retrieve your repository in the TaskRunner constructor, which again happens once, and so repo is always the same instance. Note this happens regardless of how you bind IRepository and IRepositoryFactory, see Captive Dependency post by Mark Seemann for details http://blog.ploeh.dk/2014/06/02/captive-dependency/.
In fact, if you need to create repo in the constructor, you could just inject IRepository itself. The power of the Factory extension lies in the fact that it allows to resolve instances at runtime, not construction time. For example, if your TaskRunner has Run() method, you can create repository in it, so each task to run can have its own instance.
I have this error when clicking a link on a site I'm creating
Error activating IEntityCache using binding from IEntityCache to EntityCache
No constructor was available to create an instance of the implementation type.
Activation path:
4) Injection of dependency IEntityCache into parameter entityCache of constructor of type AlbumRepository
3) Injection of dependency IAlbumRepository into parameter albumRepository of constructor of type AlbumService
2) Injection of dependency IAlbumService into parameter albumService of constructor of type AlbumController
1) Request for AlbumController
Suggestions:
1) Ensure that the implementation type has a public constructor.
2) If you have implemented the Singleton pattern, use a binding with InSingletonScope() instead.
EntityCache is a singleton with no public construction. So this is how I've done my Ninject bindings
kernel.Bind<IAlbumService>().To<AlbumService>();
kernel.Bind<IAlbumRepository>().To<AlbumRepository>();
kernel.Bind<IDbSetWrapper<Album>>().To<DbSetWrapper<Album>>();
kernel.Bind<IEntityCache>().To<EntityCache>().InSingletonScope();
What am I doing wrong?
EDIT
Here's my repository:
public AlbumRepository(DatabaseContext context, IDbSetWrapper<Album> dbSetWrapper, IEntityCache entityCache)
: base(context, dbSetWrapper, entityCache)
How do I pass in an IEntityCache?
EntityCache is a singleton with no public construction.
And how do you expect your DI framework to be able to instantiate this class? This cannot possibly work if your class doesn't have a default public constructor or a constructor taking arguments which are already registered in your DI.
You might need to provide the specific instance yourself if the class doesn't have public constructor:
kernel
.Bind<IEntityCache>()
.ToMethod(context => ...return your specific instance here...)
.InSingletonScope();
for example:
kernel
.Bind<IEntityCache>()
.ToMethod(context => EntityCache.Instance)
.InSingletonScope();