CODEWITHSUNDEEP
c#asp.net-web-apiunity-container
Jurgen Welschen
Jurgen Welschen

Reputation: 871

Unity IOC sometimes cant resolve dependency

I am having a weird problem using Unity as an IOC container and im out of ideas of what could cause it. I have a service dependency in my webapi controller but it randomly fails to resolve this dependency. Sometimes i have to start my application 3 or 4 times and then it suddenly works again.

The error I am getting is:

Resolution of the dependency failed, type = "Base.WebApi.Controllers.ApiUsersController", name = "(none)". Exception occurred while: while resolving. Exception is: InvalidOperationException - The type IApiUserService does not have an accessible constructor. ----------------------------------------------- At the time of the exception, the container was: Resolving Base.WebApi.Controllers.ApiUsersController,(none) Resolving parameter "apiUserService" of constructor Base.WebApi.Controllers.ApiUsersController(Base.BLL.Services.User.IApiUserService apiUserService) Resolving Base.BLL.Services.User.IApiUserService,(none)

For initializing and registering my types in unity i use the following:

public static void RegisterTypes(IUnityContainer container)
{
    var myAssemblies = AppDomain.CurrentDomain.GetAssemblies().Where(a => a.FullName.StartsWith("Base") && !a.FullName.StartsWith("Base.WebApi")).ToArray();

    container.RegisterType(typeof(Startup));

    container.RegisterTypes(
            UnityHelpers.GetTypesWithCustomAttribute<UnityIoCSingletonLifetimedAttribute>(myAssemblies),
            WithMappings.FromMatchingInterface,
            WithName.Default,
            WithLifetime.ContainerControlled,
            null
        ).RegisterTypes(
                UnityHelpers.GetTypesWithCustomAttribute<UnityIoCTransientLifetimedAttribute>(myAssemblies),
                WithMappings.FromMatchingInterface,
                WithName.Default,
                WithLifetime.Transient);

}

As you can see i am using singletone and transient named attributes to define the way my dependencies should be resolved.

My controller looks like this:

public class ApiUsersController : ODataController
{

    private readonly IApiUserService _apiUserService;

    public ApiUsersController(IApiUserService apiUserService)
    {
        _apiUserService = apiUserService;
    }

    public IQueryable<ApiUserEntity> Get()
    {
        return this._apiUserService.GetUsers();
    }
}

as you can see it has a dependency on user service which looks like this:

[UnityIoCTransientLifetimed]
public class ApiUserService : BaseService, IApiUserService
{
    private readonly IUserRepository _userRepository; 

    public ApiUserService(IUserRepository userRepository, IUnitOfWork uow) : base(uow)
    {
        _userRepository = userRepository;
    }
 }

The api user repository looks like this:

[UnityIoCTransientLifetimed]
public class UserRepository :  GenericRepository<ApiUserEntity>, IUserRepository
{
    public UserRepository(IUnitOfWork unitOfWork, IDomainContext context) : base(unitOfWork, context)
    {

    }

Extending the following GenericRepository:

public class GenericRepository<T> : IGenericRepository<T> where T : class
{
    protected readonly BaseContext Context;

    public GenericRepository(IUnitOfWork unitOfWork, IBaseContext context)
    {
        // register this repository with the unit of work.
        unitOfWork.Register(this);

        Context = (BaseContext)context;
    }

With my unit of work that looks like this:

[UnityIoCSingletonLifetimed]
public class UnitOfWork : IUnitOfWork
{
    private readonly Dictionary<string, IRepository> _repositories;

    // unit of work class is responsible for creating the repository and then dispossing it when no longer needed.
    public UnitOfWork()
    {
        _repositories = new Dictionary<string, IRepository>();
    }
 }

However it sometimes works and sometimes it doesnt and i cant figure out why or where to look.

Upvotes: 3

Views: 1782

Answers (1)

Jurgen Welschen
Jurgen Welschen

Reputation: 871

Finally solved it thanks to some suggestions. Looking at the documentation for 

AppDomain.CurrentDomain.GetAssemblies()

it says the following: Gets the assemblies that have been loaded into the execution context of this application domain.

Which basically means that it only loads the assemblies when they are actually needed.

The way i solved it was by using the more reliable GetReferencedAssemblies which loads all assemblies even if they are not being used.

var allAssemblies = new ReadOnlyCollection<Assembly>(
BuildManager.GetReferencedAssemblies().Cast<Assembly>().ToList());

Restarted tons of times and not one resolve crash :) Thanks everyone! For everyone looking for more information check out this SO answer: Difference between AppDomain.GetAssemblies and BuildManager.GetReferencedAssemblies

Upvotes: 1

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