Using unity DI in both web api and class library

Question

I am creating a new web api project. In this i am using two more class library projects apart from web api project Like this:

MyBlog.API (Web API project)
MyBlog.Services (Class library)- Contains additional business logic
MyBlog.Repositories (Class library) - contains all database related operations

In API project i have added the reference of Services project and in Services project i have added reference of Repositories project so API will call services and services will call repositories as this:

API > Services > Repositories

I don't want to call repositories directly form my api controllers they will be called through services. So i am not adding repository project reference in api project.

Now i am implementing unity.webapi dependency injection in my api project. Following is the code for implementing DI:

Repositories code:

namespace MyBlogs.Repositories
{
    public interface ITestRepository
    {
        string Get();
    }
}

namespace MyBlogs.Repositories
{
    public class TestRepository:ITestRepository
    {
        public string Get()
        {
            return "test";
        }
    }
}

Services code with DI implementation:

namespace MyBlogs.Services
{
    public interface ITestService
    {
        string Get();
    }
}

namespace MyBlogs.Services
{
    public class TestService : ITestService
    {
        private ITestRepository testRepository;

        public TestService(ITestRepository testRepositoryParam)
        {
            this.testRepository = testRepositoryParam;
        }

        public string Get()
        {
            return this.testRepository.Get();
        }
    }
}

Controller code:

public class ValuesController : ApiController
    {
        private ITestService testService;
        public ValuesController(ITestService testServiceParam)
        {
            this.testService = testServiceParam;
        }

        // GET api/values
        public IEnumerable<string> Get()
        {
            return new string[] { this.testService.Get() };
        }
}

and finally unityconfig file:

public static class UnityConfig
    {
        public static void RegisterComponents()
        {
            var container = new UnityContainer();
            container.RegisterType<ITestService, TestService>();

            GlobalConfiguration.Configuration.DependencyResolver = new UnityDependencyResolver(container);
        }
    }

Now i am facing the issue here, as i have not added repository project reference in api project where i have this unityconfig file so how can i register ITestRepository and TestRepository in unity similart to ITestService and TestService?? Is there any way i could register my repository project's dependencies somewhere else without adding the project reference?? or if i will try to add unity in services project then how will it gets registered??

I have registered unityConfig in global.asax of web api project:

protected void Application_Start()
        {
            UnityConfig.RegisterComponents();
        }

mmm .. i think you have to call the Unity in a webapi project or a console project.. — federico scamuzzi
– federico scamuzzi, Commented Jan 6, 2017 at 10:27
in theory you can define another Unity config in MyBlogs.Services assembly which does know of repository and register it as well. doing that you would not have a reference from webapi to repository make another UnityConfig in MyBlogs.Services register your repository types there and then ServicesUnityConfig.RegsiterComponents() UnityConfig.RegisterComponents(); — eran otzap
– eran otzap, Commented Jan 6, 2017 at 10:30

eran otzap · Accepted Answer · 2017-01-06 10:38:47Z

2

That's a good question and i haven't done this myself with unity. Autofac, Windsor and other DI's let you expose modules or installers from each assembly and then you load modules from other assemblies that do reference them.

so i'm just going to propose a general solution based on that idea. (Hope this can work :) )

public static class WebApiUnityConfig
{
    public static void RegisterComponents()
    {
        var container = new UnityContainer();
        container.RegisterType<ITestService, TestService>();

        GlobalConfiguration.Configuration.DependencyResolver = new UnityDependencyResolver(container);
    }
}   


public static class ServicesUnityConfig
{
    public static void RegisterComponents()
    {
        var container = new UnityContainer();
        container.RegisterType<ITestRepository, TestRepository>();

        GlobalConfiguration.Configuration.DependencyResolver = new UnityDependencyResolver(container);
    }
}   


protected void Application_Start()
{
     ServiceUnityConfig.RegisterComponents();
     WebApiUnityConfig.RegisterComponents();
}

edited Jan 6, 2017 at 10:38

answered Jan 6, 2017 at 10:36

eran otzap

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4 Comments

Ankit K Over a year ago

Based on your idea i have created a unity file in service project and called its RegisterComponents method directly from unity file of api project by passing same UnityContainer as a parameter to service's unity file like this: Following line added in api project's unity config: ServiceUnityConfig.RegisterComponents(container);

Ankit K Over a year ago

And following is service's unity config file:public static class ServiceUnityConfig { public static void RegisterComponents(UnityContainer container) { container.RegisterType<ITestRepository, TestRepository>(); } } It solved my problem. Thanks.

eran otzap Over a year ago

well if it solved the problem you should accept the answer

iGanja Over a year ago

Didn't really "solve" the problem, but certainly put us on the right track to an actual solution.

Ankit K · Accepted Answer · 2017-01-09 04:21:06Z

1

I solved it by creating a unity file in service project and called its RegisterComponents method directly from unity file of api project by passing same UnityContainer as a parameter to service's unity file like this:

public static class UnityConfig
{
    public static void RegisterComponents()
    {
    var container = new UnityContainer();

        container.RegisterType<ITestService, TestService>();
        ServiceUnityConfig.RegisterComponents(container);

        GlobalConfiguration.Configuration.DependencyResolver = new UnityDependencyResolver(container);
    }
}

public static class ServiceUnityConfig
{
    public static void RegisterComponents(UnityContainer container)
    {
        container.RegisterType<ITestRepository, TestRepository>();
    }
}

It solved my problem without registering unity two times in app_start. Thanks for above answer of eran, based on above answer i implemented it like this.

answered Jan 9, 2017 at 4:21

Ankit K

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1 Comment

iGanja Over a year ago

Gonna have to say, this is the best answer I have run across so far. The problem I was trying to solve was how to decouple the reference from the api project to the repository project. Since there is no concept of main, or app_start in a class library, how does one accomplish this? Well, this works, and until I find a better way, this is the solution.

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