How to use Ninject bootstrapper in WebApi OwinHost Startup?

Question

I am migrating from IIS WebAPI to OwinHost. Utilizing the latest pre-release versions of nuget packages, I successfully used instructions here:

https://github.com/ninject/Ninject.Web.Common/wiki/Setting-up-a-OWIN-WebApi-application

Here is stub of my code:

    public void Configuration(IAppBuilder app)
    {
        var config = new HttpConfiguration();
        config.MapHttpAttributeRoutes();

        app.UseNinjectMiddleware(CreateKernel);
        app.UseNinjectWebApi(config);
    }

    private static StandardKernel CreateKernel()
    {
        var kernel = new StandardKernel();
        kernel.Load(Assembly.GetExecutingAssembly());
        RegisterServices(kernel);
        return kernel;
    }

    private static void RegisterServices(IKernel kernel)
    {
        ...
    }

But in my code and the documentation example, the Ninject kernel is not created until after Startup. I need Ninject DI, however, in the Startup registration process for Cors and OAuth middleware registration. Before migrating to OwinHost, I could do something like this:

public void Configuration(IAppBuilder app)
{
  _bootstrapper = new Bootstrapper();
  _bootstrapper.Initialize(CreateKernel);           

  var config = new HttpConfiguration();
  config.MapHttpAttributeRoutes();

  // USE _boostrapper.Kernel here

  app.UseNinjectMiddleware(CreateKernel);
  app.UseNinjectWebApi(config);
}

But internally, OwinBootstrapper.Execute will end up calling CreateKernel and bootstrapper.Initialize a second time, with bad consequences.

What is the right way to create and use the ninject kernel within Startup and still register the Ninject/WebAPI middleware?

Solution 1

Add the following nuget-packages to your application:

1. Install-Package Microsoft.AspNet.WebApi.Owin
2. Install-Package Ninject

If you are using web api version 5.0.0.0 you also need to download the Ninject Resolver class from the repo to avoid compatability issues.

Create a static method that returns a Kernel object

public static class NinjectConfig
{
    public static IKernel CreateKernel()
    {
        var kernel = new StandardKernel();
        //Create the bindings
        kernel.Bind<IProductsRepository>().To<ProductRepository>();
        return kernel;
    }
}

Then you can use ninject in your startup class

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        var config = new HttpConfiguration();
        config.DependencyResolver = new NinjectResolver(NinjectConfig.CreateKernel());

        config.Routes.MapHttpRoute("default", "api/{controller}/{id}", new { id=RouteParameter.Optional });

        app.UseWebApi(config);
    }
}

Solution 2

Create the kernel manually and then make UseNinjectMiddleware use the same one instead of creating another.

public void Configuration(IAppBuilder app)
{
  var kernel = CreateKernel()

  var config = new HttpConfiguration();
  config.MapHttpAttributeRoutes();

  // USE kernel here

  app.UseNinjectMiddleware(() => kernel);
  app.UseNinjectWebApi(config);
}

Comments

[Ricardo Huertas]

I tried a lot of combinations to make my Owin + WebApi works. I was able to solve it thanks to you. The only package missing on your answer is the Ninjec.Web.Common. Thanks a lot.

[jao]

Thanks for such a great answer! Was looking for this for a long time!

[CrazyPyro]

config.DependencyResolver = new NinjectResolver(new Ninject.Web.Common.Bootstrapper().Kernel); This is the only solution that worked for me! Trying to use app.UseNinjectMiddleware and app.UseNinjectWebApi were giving me "InvalidOperationException: Sequence contains no elements" no matter what I did. Also, instead of "download the Ninject Resolver class from the repo" I just installed NuGet package for WebApiContrib.IoC.Ninject

[Sai Kumar]

This worked for me, I just called Resolver at the end of statup.cs Configuration functions. config.DependencyResolver = new NinjectHttpDependencyResolver(new Ninject.Web.Common.Bootstrapper().Kernel); NinjectHttpDependencyResolver is my resolver class