Factory Summary and Runtime Inversion Control

Question

I have the following class and interface structure, and I have a hard time trying to get the code to do what I need.

public interface IUserManager
{
    int Add(User user);
}

public class UserManagerA : IUserManager{}
public class UserManagerB : IUserManager{}

In this example, I use Ninject as an IoC container, but I am open to changing it if any other container solves the problem:

This is inside of mine NinjectWebCommon.cs:

void RegisterServices(IKernel kernel)
{
    string userRole = CurrentUser.Role;//this gets the user logged in
    //This is the part I do not how to do
    //I wish I could just type this in:
    kernel.Bind<IUserManager>().To<UserManagerA>()
        .When(userRole == "RoleA"); // this doesn't work obviously
    kernel.Bind<IUserManager>().To<UserManagerB>()
        .When(userRole == "RoleB"); // same doesn't work
}

All this so that in my (MVC) controller I can do this:

public class UserController
{
    private readonly IUserManager _userManager;
    public UserController(IUserManager userManager)
    {
        _userManager = userManager;
    }
    public ActionResult Add(User user)
    {
        //this would call the correct manager
        //based on the userRole
        _userManager.Add(user);
    }
}

I read articles about abstract Factory, but did not find one that explains how to integrate Factory with the IoC container and pass the parameter received at runtime to allow implementations.

Answer 1

IUserManager ( 100 ), UserManager , .

-, IUserManager .

public interface IUserManager
{
    int Add(User user);
    bool AppliesTo(string userRole);
}

public class UserManagerA : IUserManager
{
    // Add method omitted

    public bool AppliesTo(string userRole)
    {
        // Note that it is entirely possible to 
        // make this work with multiple roles and/or
        // multiple conditions.
        return (userRole == "RoleA");
    }
}

public class UserManagerB : IUserManager
{
    // Add method omitted

    public bool AppliesTo(string userRole)
    {
        return (userRole == "RoleB");
    }
}

, userRole. IUserManager DI, .

public interface IUserManagerStrategy
{
    IUserManager GetManager(string userRole);
}

public class UserManagerStrategy
    : IUserManagerStrategy
{
    private readonly IUserManager[] userManagers;

    public UserManagerStrategy(IUserManager[] userManagers)
    {
        if (userManagers == null)
            throw new ArgumentNullException("userManagers");

        this.userManagers = userManagers;
    }

    public IUserManager GetManager(string userRole)
    {
        var manager = this.userManagers.FirstOrDefault(x => x.AppliesTo(userRole));
        if (manager == null && !string.IsNullOrEmpty(userRole))
        {
            // Note that you could optionally specify a default value
            // here instead of throwing an exception.
            throw new Exception(string.Format("User Manager for {0} not found", userRole));
        }

        return manager;
    }
}

public class SomeService : ISomeService
{
    private readonly IUserManagerStrategy userManagerStrategy;

    public SomeService(IUserManagerStrategy userManagerStrategy)
    {
        if (userManagerStrategy == null)
            throw new ArgumentNullException("userManagerStrategy");
        this.userManagerStrategy = userManagerStrategy;
    }

    public void DoSomething()
    {
        string userRole = CurrentUser.Role;//this gets the user logged in

        // Get the correct UserManger according to the role
        IUserManager userManager = this.userManagerStrategy.GetManger(userRole);

        // Do something with userManger
    }
}

void RegisterServices(IKernel kernel)
{
    kernel.Bind<IUserManager>().To<UserManagerA>();
    kernel.Bind<IUserManager>().To<UserManagerB>();

    // Ninject will automatically supply both IUserManager instances here
    kernel.Bind<IUserManagerStrategy>().To<UserManagerStrategy>();

    kernel.Bind<ISomeService>().To<SomeService>();
}

, . .

, case switch, , UserManager. UserManager UserManager , , DI.

, , DI .

CurrentUserProvider RagtimeWilly , .

: StructureMap

Answer 2

, UserManager, :

public class UserManagerProvider : IUserManagerProvider
{
    private readonly IContext _context;

    public UserManagerProvider(IContext context)
    {
        _context = context;
    }

    public IUserManager Create(User currentUser)
    {
        if (currentUser.Role == "User A")
            return _context.Kernel.Get<UserManagerA>();

        if (currentUser.Role == "User B")
            return _context.Kernel.Get<UserManagerB>();

        // Or bind and resolve by name
        // _context.Kernel.Get<IUserManager>(currentUser.Role);
    }
}

:

private readonly IUserManager _userManager;

public UserController(IUserManagerProvider userManagerProvider)
{
    _userManager = userManagerProvider.Create(CurrentUser);
}

, , , CurrentUserProvider . , unit test, , :

private readonly IUserManager _userManager;
private readonly User _currentUser;

public UserController(IUserManagerProvider userManagerProvider, ICurrentUserProvider currentUserProvider)
{
    _currentUser = currentUserProvider.GetUser();
    _userManager = userManagerProvider.Create(_currentUser);
}