Conditional Resolving in Unity Dependency Injection

Conditional resolving allows the container to resolve and inject different implementations of an interface based on specific criteria. In this case, we aim to use Unity to conditionally resolve different authentication mechanisms based on the type of authentication used (e.g., Twitter, Facebook, etc.).

Interfaces

Define an IAuthenticate interface to represent the authentication behavior. Add an AppliesTo method to check if the provider applies to the specified provider name.

public interface IAuthenticate
{
    bool Login(string user, string pass);
    bool AppliesTo(string providerName);
}

Authentication Providers

Create separate classes (e.g., TwitterAuth and FacebookAuth) that implement IAuthenticate and contain the specific authentication logic. In the AppliesTo method, determine if the provider is applicable based on the provided provider name.

public class TwitterAuth : IAuthenticate
{
    bool Login(string user, string pass) { /* Logic to connect to Twitter API */ }
    bool AppliesTo(string providerName) { return this.GetType().Name.Equals(providerName); }
}

Strategy

Implement an IAuthenticateStrategy interface to encapsulate the conditional resolution logic. Inject an array of IAuthenticate providers and use the AppliesTo method to select the correct provider for authentication.

public interface IAuthenticateStrategy
{
    bool Login(string providerName, string user, string pass);
}

public class AuthenticateStrategy : IAuthenticateStrategy
{
    private readonly IAuthenticate[] _authenticateProviders;

    public AuthenticateStrategy(IAuthenticate[] authenticateProviders) => _authenticateProviders = authenticateProviders;

    public bool Login(string providerName, string user, string pass)
    {
        var provider = _authenticateProviders.FirstOrDefault(x => x.AppliesTo(providerName));

        if (provider == null)
        {
            throw new Exception("Login provider not registered");
        }

        return provider.Login(user, pass);
    }
}

Unity Registration

Register the authentication providers and the strategy with Unity, specifying the provider names for conditional resolution.

unityContainer.RegisterType<IAuthenticate, TwitterAuth>("twitterAuth");
unityContainer.RegisterType<IAuthenticate, FacebookAuth>("facebookAuth");
unityContainer.RegisterType<IAuthenticateStrategy, AuthenticateStrategy>(
    new InjectionConstructor(
        new ResolvedArrayParameter<IAuthenticate>(
            new ResolvedParameter<IAuthenticate>("twitterAuth"),
            new ResolvedParameter<IAuthenticate>("facebookAuth")
        )
    ));

Usage

In the controller, inject the IAuthenticateStrategy and use it to perform conditional authentication based on the provider name.

public AuthenticateController(IAuthenticateStrategy authenticateStrategy)
{
    if (authenticateStrategy == null)
        throw new ArgumentNullException(nameof(authenticateStrategy));

    _authenticateStrategy = authenticateStrategy;
}

public virtual ActionResult Twitter(string user, string pass)
{
    bool success = _authenticateStrategy.Login("TwitterAuth", user, pass); /* Authenticate using Twitter */
}

public virtual ActionResult Facebook(string user, string pass)
{
    bool success = _authenticateStrategy.Login("FacebookAuth", user, pass); /* Authenticate using Facebook */
}

unity.config

Alternatively, you can perform the Unity registration in the unity.config file.

<register type="IAuthenticate" mapTo="TwitterAuth" name="twitterAuth" />
<register type="IAuthenticate" mapTo="FacebookAuth" name="facebookAuth" />
<register type="IAuthenticateStrategy" mapTo="AuthenticateStrategy" />

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