Change injected object at runtime

Question

I want to have multiples implementation of the IUserRepository each implementation will work with a database type either MongoDB or any SQL database. To do this I have ITena

Answer 1

You can try injecting a factory rather than the actual repository. The factory will be responsible for building the correct repository based on the current user identity.

It might require a little more boiler plate code but it can achieve what you want. A little bit of inheritance might even make the controller code simpler.

Answer 2

You should define a proxy implementation for IUserRepository and hide the actual implementations behind this proxy and at runtime decide which repository to forward the call to. For instance:

public class UserRepositoryDispatcher : IUserRepository
{
    private readonly Func<bool> selector;
    private readonly IUserRepository trueRepository;
    private readonly IUserRepository falseRepository;

    public UserRepositoryDispatcher(Func<bool> selector,
        IUserRepository trueRepository, IUserRepository falseRepository) {
        this.selector = selector;
        this.trueRepository = trueRepository;
        this.falseRepository = falseRepository;
    }

    public string Login(string username, string password) {
        return this.CurrentRepository.Login(username, password);
    }

    public string Logoff(Guid id) {
        return this.CurrentRepository.Logoff(id);
    }

    private IRepository CurrentRepository {
        get { return selector() ? this.trueRepository : this.falseRepository;
    }
}

Using this proxy class you can easily create a runtime predicate that decides which repository to use. For instance:

services.AddTransient<IUserRepository>(c =>
    new UserRepositoryDispatcher(
        () => c.GetRequiredService<ITenant>().DataBaseName.Contains("Mongo"),
        trueRepository: c.GetRequiredService<UserMongoRepository>()
        falseRepository: c.GetRequiredService<UserSqlRepository>()));