OK, so I've been working on this for hours. I've found a couple of posts here, but nothing that actually resolves the problem. So, let me try it again...
I have an MVC2 app using Ninject and a custom membership provider.
If I try and inject the provider using the ctor, I get an error: 'No parameterless constructor defined for this object.'
public class MyMembershipProvider : MembershipProvider
{
IMyRepository _repository;
public MyMembershipProvider(IMyRepository repository)
{
_repository = repository;
}
I've also been playing around with factories and Initialize(), but everything is coming up blanks.
Any thoughts/examples?
The Membership provider model can only instantiate a configured provider when it has a default constructor. You might try this using the Service Locator pattern, instead of using Dependency Injection. Example:
public class MyMembershipProvider : MembershipProvider
{
IMyRepository _repository;
public MyMembershipProvider()
{
// This example uses the Common Service Locator as IoC facade, but
// you can change this to call NInject directly if you wish.
_repository = ServiceLocator.Current.GetInstance<IMyRepository>;
}
This is how I was able to do this:
1) I created a static helper class for Ninject
public static class NinjectHelper
{
public static readonly IKernel Kernel = new StandardKernel(new FooServices());
private class FooServices : NinjectModule
{
public override void Load()
{
Bind<IFooRepository>()
.To<EntityFooRepository>()
.WithConstructorArgument("connectionString",
ConfigurationManager.ConnectionStrings["FooDb"].ConnectionString);
}
}
}
2) Here is my Membership override:
public class FooMembershipProvider : MembershipProvider
{
private IFooRepository _FooRepository;
public FooMembershipProvider()
{
NinjectHelper.Kernel.Inject(this);
}
[Inject]
public IFooRepository Repository
{
set
{
_FooRepository = value;
}
}
...
With this approach it doesn't really matter when the Membership provider is instantiated.
I had the same problem at the exact same spot in the book. It wasn't until later on in the book that I noticed there were two separate web.config files. I initially placed my connectionString key in the wrong web.config file. It wasn't until I placed the connectionString in the correct web.config file that the 'no parameterless constructor' error went away.
Related
Trying to wrap my head around dependency injection, coming from the world of static classes and instantiated classes. Here is what I currently have:
[SomeFilter]
public class AController : Controller
{
private readonly IOptions<AppSettings> _appSettings;
public AController(IOptions<AppSettings> appSettings)
{
_appSettings = appSettings;
}
// GET: /characters/
public IActionResult Index()
{
//do something
}
SomeFilter gets called immediately, and does this:
public class SomeFilter: ActionFilterAttribute, IActionFilter
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
OtherClass.RunMe();
}
}
OtherClass looks like this:
public class OtherClass
{
private readonly IOptions<AppSettings> _appSettings;
public OtherClass(IOptions<AppSettings> appSettings)
{
_appSettings = appSettings;
}
public RunMe()
{
//do something
}
I also have OtherClass registered as a service.Singleton in the Startup.cs.
I get an error stating:
"An object reference is required for a non-static field"
for the OtherClass.RunMe(); call.
I was under the assumption that I can call this class from anywhere within my code instead of having to create a new instance of it? Essentially, how do I call methods from other classes using dependency injection?
You can't constructor injection on filters. It's all about run time order. When you try injection on constructor, your IoC container not reachable at the moment. You should be use property/setter injection.
I prefer using structuremap container for to do this. Because structuremap has very easy to apply any type injection. For example when you have a filter registry like this
public class ActionFilterRegistry : Registry
{
public ActionFilterRegistry(Func<IContainer> containerFactory)
{
For<IFilterProvider>().Use(
new StructureMapFilterProvider(containerFactory));
Policies.SetAllProperties(x =>
x.Matching(p =>
p.DeclaringType.CanBeCastTo(typeof(ActionFilterAttribute)) &&
p.DeclaringType.Namespace.StartsWith("YourNameSpace") &&
!p.PropertyType.IsPrimitive &&
p.PropertyType != typeof(string)));
}
}
And you register it on your global.asax(prefer) or one of your startup class.
Example app_Start method.
DependencyResolver.SetResolver(new StructureMapDependencyResolver(() => Container ?? ObjectFactory.Container));
ObjectFactory.Container.Configure(cfg =>
{
cfg.AddRegistry(new StandardRegistry());
cfg.AddRegistry(new ControllerRegistry());
cfg.AddRegistry(new ActionFilterRegistry(() => Container));
cfg.AddRegistry(new MvcRegistry());
});
Then you can use any filter with injection. But pay attention you shouldn't be use contructor injection like you do.
I found a way to inject into the filter by using
[ServiceFilter(typeof(MyFilter))]
instead of just
[MyFilter]
and within the filter's
(ActionExecutingContext context)
{
var controller = context.Controller as Controller.
controller.whateverIneed
}
This now provides me with what I need within the filter. What I also realized is that I can't remove the need for creating references to other classes using new, as I was under the impression Core's dependency was all about "no more new". This gets into fundamentals with Core which I'm still grasping with.
What I ended up doing was creating new classes that do some work, but they are setup as services and registered in the startup.cs. I'm still grappling on how to intermingle registered services (which I can inject) and new instances of worker classes (which usually hold static information), and passing information between them all.
In my application i configured structuremap like
public class DefaultRegistry : Registry {
#region Constructors and Destructors
public DefaultRegistry() {
Scan(
scan => {
scan.Assembly("Eterp.Data.ErpCore");
scan.Assembly("Eterp.Data.Seed");
scan.Assembly("Eterp.Application.ErpCore");
scan.TheCallingAssembly();
scan.WithDefaultConventions();
});
ForConcreteType<AclAuthorizationManager>().Configure.Ctor<IResourceOperationAppService>()
}
#endregion
}
And i have class
public class AclAuthorizationManager : ClaimsAuthorizationManager
{
private readonly IResourceOperationAppService _resourceOperationAppService;
public AclAuthorizationManager(IResourceOperationAppService resourceOperationAppService)
{
_resourceOperationAppService = resourceOperationAppService;
}
public override bool CheckAccess(AuthorizationContext context)
{
var isCurrentUserAuthorized = context.Principal.Identity.IsAuthenticated;
return isCurrentUserAuthorized && _resourceOperationAppService.CanAccessResource(context.Action.FirstOrDefault().Value, context.Principal.Claims);
}
}
This class is custom claim authorization class using in my application, but when i exceuting the application,i am getting an error which related to lack of parameter required by the constructor, ( This class has constructor with parameter type IResourceOperation). but i already configured all the details in structureMap . i am sure that my structuremap configuration is working 100% well expect the creation of this AclAuthorizationManager class.because i am able to to apply DI in other classes.
What is wrong part in my code?
in my experience when you specify the type constructor must say that inherits from the interface.
Therefore, you should replace this line:
ForConcreteType<AclAuthorizationManager>().Configure.Ctor<IResourceOperationAppService>()
By:
ForConcreteType<AclAuthorizationManager>().Configure.Ctor<IResourceOperationAppService>().Is<ResourceOperationAppService>()
Where is the implementation ResourceOperationAppService IResourceOperationAppService.
I'm using SignalR 0.5.2 and I'm trying to get a DependencyResolver set up using Unity. I've written the simplest code I can. I have a hub that I'm trying to inject into which looks like this:
public class SimpleHub : Hub
{
private readonly ITestService _service;
public SimpleHub(ITestService service)
{
_service = service;
}
public void Update()
{
Clients.callback("Kevin");
}
}
and a DependencyResolver that looks like this:
public class UnityDependencyResolver : DefaultDependencyResolver
{
private readonly IUnityContainer _container;
public UnityDependencyResolver(IUnityContainer container)
{
_container = container;
}
public override object GetService(Type serviceType)
{
if (_container.IsRegistered(serviceType))
{
return _container.Resolve(serviceType);
}
return base.GetService(serviceType);
}
public override IEnumerable<object> GetServices(Type serviceType)
{
if (_container.IsRegistered(serviceType))
{
return _container.ResolveAll(serviceType);
}
return base.GetServices(serviceType);
}
}
I register the dependency resolver in Global.asax
protected void Application_Start()
{
IUnityContainer container = new UnityContainer();
InitializeContainer(container);
SignalR.IDependencyResolver resolver = new UnityDependencyResolver(container);
GlobalHost.DependencyResolver = resolver;
RouteTable.Routes.MapHubs();
// more MVC stuff here
}
where InitializeContainer register the ITestService in Unity
The resolver "works" in that it's getting called for all the SignalR types, and if I leave my hub with a default constructor it all gets loaded. However the resolver never gets asked to resolve the ITestService interface.
I've also tried passing the resolver to MapHubs, still no luck. I've also tried property injection using the [Dependency] attribute and that didn't work either.
Do I need to register the resolver with MVC as well? (I have tried that by implementing both IDependecyResolver interfaces but get an exception telling me the resolver doesn't implement IServiceLocator)
So I've sort of fixed this. I wondered if the fact that the Hub was registered with the signalr container and the interface was registered with the Unity container was causing the issue. So I registered the Hub with Unity and then everything works.
This sort of makes sense as there are two containers.
Is this the standard behaviour?
In case someone else is wondering... I found a good SPA example that uses
SignalR 1.0.1
Unity 3
A bunch of other frameworks
The interesting thing is the way he create the container, the dependencies and everything else. Worth checking it out.
This is my first try using DI, I've chosen ninject for it's reportedly easy learning curve, and have this question.
I'm creating objects like this:
var registrants = JsonConvert.DeserializeObject<List<Registrant>>(input);
I currently have this constructor for Registrant
[Inject]
public Registrant(IMemberRepository memberRepository)
{
_memberRepository = memberRepository;
}
What is the best way to have the repository dependency be injected into the deserialized object(s) using Ninject?
You can't use constructor injection with objects that are not created by Ninject (e.g. deserialized objects). But you can use property injection. Just call kernel.Inject(obj)
One question that remains is why you want to inject those objects. Normally, you don't want to use depedency injection on data container objects. In a proper design they don't have any dependency on services. The operations that need to be done on the services are done by the owner of the data container objects. I recommend to consider a refactoring of your design.
Assuming you're using Ninject V2, and you're using it in the context of an ASP.NET app, you should be using Ninject.Web to do the hookups.
Then you set up a Global class with the Factory Method support hooked in:
public class Global : NinjectHttpApplication
{
protected override Ninject.IKernel CreateKernel()
{
var kernel = new StandardKernel( new Module() );
kernel.Components.Add( new FuncModule( ) );
return kernel;
}
}
that registers the module that will Bind IMemberRepository to something:
public class Module : NinjectModule
{
public override void Load()
{
Bind<IMemberRepository>().To<MemberRepository>();
}
}
and the page wires up like this:
public class ThePage : PageBase
{
readonly Func<Registrant> _createRegistrant;
public ThePage( Func<Registrant> createRegistrant )
{
_createRegistrant = createRegistrant;
}
private void OnCreateRegistrant()
{
var newRegistrant = _createRegistrant();
}
}
NB not 100% sure if constructor injection is supported for Web Forms pages or wheter the above needs to drop to property injection... anyone?
(assuming the classes you have are as follows:)
public class MemberRepository : IMemberRepository
{
}
public interface IMemberRepository
{
}
public class Registrant
{
private readonly IMemberRepository _memberRepository;
public Registrant( IMemberRepository memberRepository )
{
_memberRepository = memberRepository;
}
}
Well, it seems like I'm stuck in my application structure. Here's what I want to do:
UI layer: An ASP.NET webforms website.
BLL: Business logic layer which calls the repositories on DAL.
DAL: .EDMX file (Entity Model) and ObjectContext with Repository classes which abstract the CRUD operations for each entity.
Entities: The POCO Entities. Persistence Ignorant. Generated by Microsoft's ADO.Net POCO Entity Generator.
I'd like to create an obejctcontext per HttpContext in my repositories to prevent performance/thread [un]safety issues. Ideally it would be something like:
public MyDBEntities ctx
{
get
{
string ocKey = "ctx_" + HttpContext.Current.GetHashCode().ToString("x");
if (!HttpContext.Current.Items.Contains(ocKey))
HttpContext.Current.Items.Add(ocKey, new MyDBEntities ());
return HttpContext.Current.Items[ocKey] as MyDBEntities ;
}
}
The problem is the I don't want to access HttpContext in my DAL (Where the repositories are located). But I have to somehow pass HttpContext to DAL. based on the answer to my question here, I have to use IoC pattern. Ideally I'd like to achieve something like this in amulti-layered architecture.
I've checked out Autofac and it seems very promising. But I'm not sure how could I achieve this (Passing Httpcontext to make sure one ObjectContext is instantiated per HttpContext) in a multi-layered architecture. Could anyone give me some working example on how to achieve this? How can I be aware of HttpContext in DAL without directly accessing the HttpContext in DAL? I feel like I'm a bit lost in designing a multi-layered solution.
I have never used IoC container with WebForms so get this as some high level solution which should probably be futher improved.
You can try creating some IoC provider as singleton:
public class IoCProvider
{
private static IoCProvider _instance = new IoCProvider();
private IWindsorContainer _container;
public IWindsorContainer
{
get
{
return _container;
}
}
public static IoCProvider GetInstance()
{
return _instance;
}
private IoCProvider()
{
_container = new WindsorContainer(new XmlInterpreter(new ConfigResource("castle")));
}
}
Your web.config will have to contain sections like (the configuration is based on your previous post):
<configuration>
<configSections>
<section name="castle" type="Castle.Windsor.Configuration.AppDomain.CastleSectionHandler, Castle.Windsor" />
</configSections>
<castle>
<components>
<component id="DalLayer"
service="MyDal.IDalLayer, MyDal"
type="MyDal.MyDalLayer, MyDal"
lifestyle="PerWebRequest">
<!--
Here we define that lifestyle of DalLayer is PerWebRequest so each
time the container resolves IDalLayer interface in the same Web request
processing, it returns same instance of DalLayer class
-->
<parameters>
<connectionString>...</connectionString>
</parameters>
</component>
<component id="BusinessLayer"
service="MyBll.IBusinessLayer, MyBll"
type="MyBll.BusinessLayer, MyBll" />
<!--
Just example where BusinessLayer receives IDalLayer as
constructor's parameter.
-->
</components>
</castle>
<system.Web>
...
</system.Web>
</configuration>
Implementation of these interfaces and classes can look like:
public IDalLayer
{
IRepository<T> GetRepository<T>(); // Simplified solution with generic repository
Commint(); // Unit of work
}
// DalLayer holds Object context. Bacause of PerWebRequest lifestyle you can
// resolve this class several time during request processing and you will still
// get same instance = single ObjectContext.
public class DalLayer : IDalLayer, IDisposable
{
private ObjectContext _context; // use context when creating repositories
public DalLayer(string connectionString) { ... }
...
}
public interface IBusinessLayer
{
// Each service implementation will receive necessary
// repositories from constructor.
// BusinessLayer will pass them when creating service
// instance
// Some business service exposing methods for UI layer
ISomeService SomeService { get; }
}
public class BusinessLayer : IBusinessLayer
{
private IDalLayer _dalLayer;
public BusinessLayer(IDalLayer dalLayer) { ... }
...
}
Than you can define base class for your pages and expose the business layer (you can do the same with any other class which can be resolved):
public abstract class MyBaseForm : Page
{
private IBusinessLayer _businessLayer = null;
protected IBusinessLayer BusinessLayer
{
get
{
if (_businessLayer == null)
{
_businessLayer = IoCProvider.GetInstance().Container.Resolve<IBusinessLayer>();
}
return _businessLayer;
}
...
}
Complex solution whould involve using custom PageHandlerFactory to resolve pages directly and inject dependencies. If you want to use such solution check Spring.NET framework (another API with IoC container).