Ninject Contextual Binding by ParentRequest

Question

I am new to using Ninject and applying Dependency Injection to my code. As a result I want to make sure I am not over complicating the solution or undermining the benefits of using Ninject and Dependency Injection.

The following code is a simplified conceptual example of what I am trying to accomplish. I am wondering if if there is a better way to to produce the same result or if I should look at modifying my design. I understand that an alternative solution would be to supply the context to IService and IProvider via method injection and use the WhenInjectedInto method but that would go against how I am trying to use the interface.

    public interface IContext
    {
    }

    public interface IProvider
    {
        IContext Context { get; }
    }

    public interface IService
    {
        IProvider Provider { get; }
    }

    public interface IBindingContext
    {
        IService Service { get; }
    }

    public CreateBindings()
    {
        this.kernel = new StandardKernel();
        this.kernel.Bind<IContext>().To<GenericContext>();
        this.kernel.Bind<IProvider>().To<GenericProvider>();
        this.kernel.Bind<IService>().To<GenericService>();

        // Do not want to create specific implementations
        //this.kernel.Bind<IContext>().To<SpecificContext>().WhenInjectedInto<SpecificProvider>();
        //this.kernel.Bind<IProvider>().To<SpecificProvider>().WhenInjectedInto<SpecificService>();
        //this.kernel.Bind<IService>().To<SpecificService>().WhenInjectedExactlyInto<SpecificBindingContext>();

        this.kernel.Bind<IContext>().To<SpecificContext>().When(x => this.IsUsedBy<SpecificBindingContext>(x));
    }

    private bool IsUsedBy<T>(IRequest request)
    {
        if (request == null)
            return false;

        if (request.Service == typeof(T))
            return true;

        if (this.IsUsedBy<T>(request.ParentRequest))
                return true;

        return false;
    }

The actual interfaces that I am dealing with are:

public interface ILogDirectory
{
    string FullPath { get; }
}

public interface ILogProvider
{
    void Write(string text);
}

public interface ILogService
{
    void Write(Exception exception);

    void Write(string text);

    void WriteDebug(string text);
}

The issue I have is that I don't want the client code to know how or where information is being logged. If I create Write methods that include a signature for ILogDirectory I would be exposing to many implementation details. At this point I can actually create the context specific log implementations pretty easily but the only thing that is unique for each implementation is the directory that contains the log files. As a result I would rather not have to create the context specific implementations for each interface.

Dave Thieben Dave Thieben · Accepted Answer · 2015-03-09T16:39:40

I think what you want is contextual binding:

https://github.com/ninject/Ninject/wiki/Contextual-Binding

if you have a more complicated scenario, you can also use a provider:

https://github.com/ninject/Ninject/wiki/Providers%2C-Factory-Methods-and-the-Activation-Context

Ninject Contextual Binding by ParentRequest

1 Answers