Inject different implementations that have same interface in multiple constructor parameters

Question

My goal is to create an object that contains different implementations of an interface and at runtime select the implementation to use. I'm using the Dependency injection in ASP.NET Core.

Code:

public interface IStateRepository : IDbReadRepository<IState> { }

public interface IDbReadRepository<T> : IBaseRepository
{
     IReadOnlyList<T> GetAll();
}

public interface IBaseRepository
{
    IUserContext UserContext { get; set; }
}

namespace MvcOpinionatedTemplate.Repositories.Dapper
{
    public class StateRepository : BaseDbRepository, IStateRepository
    {
        public StateRepository(IUserContext userContext, IDbConnection dbConnection) : base(userContext, dbConnection) { }

        public IReadOnlyList<IState> GetAll()
        {
            return _dbConnection.Query<State>("SELECT * FROM State").ToList();
        }
    }
}

namespace Template.Repositories.Local
{
    public class StateRepository : BaseRepository, IStateRepository
    {
        public StateRepository(IUserContext userContext) : base(userContext) { }

        public IReadOnlyList<IState> GetAll()
        {
            var filePath = Path.Combine(AppContext.BaseDirectory, @"Local\json\states.json");

            return JsonConvert.DeserializeObject<List<State>>(File.ReadAllText(filePath));
        }
}


namespace MvcOpinionatedTemplate.Repositories.Collections
{
    public class StateRepositories
    {
        public IStateRepository Local { get; }

        public IStateRepository SqlServer { get; }

        public StateRepositories(IStateRepository local, IStateRepository sqlServer)
        {
            Local = local;
            SqlServer = sqlServer;
        }
    }
}

What I'd like to do is set in the Startup.ConfigureServices():

services.AddTransient<StateRepositories, XXXXX>

I tried this:

services.AddTransient<StateRepositories>(s => new StateRepositories(new Repositories.Local.StateRepository(--UserContext--), new Repositories.Dapper.StateRepository(-UserContext--)));

The problem is how to have DI populate UserContext. I have it defined Startup.ConfigureServices():

services.AddScoped<IUserContext, UserContext>();

How do have DI populate UserContext for the StateRepositories implementations? Or is there a better approach to achieve my goal?

Possible duplicate of [Injecting multiple implementations with Dependency injection](https://stackoverflow.com/questions/40946320/injecting-multiple-implementations-with-dependency-injection) — Camilo Terevinto, Jul 20 '18 at 23:06

score 4 · Accepted Answer · answered Jul 21 '18 at 07:16

You can register your IStateRepository separately and then inject IEnumerable<IStateRepository> which injects all implementations of IStateRepository.

public interface IStateRepository
{
}

public class LocalRepository : IStateRepository
{
}

public class DapperRepository : IStateRepository
{
}

services.AddTransient<IStateRepository, LocalRepository>()
        .AddTransient<IStateRepository, DapperRepository>()
        .AddTransient<StateRepositories>();

public class StateRepositories
{
    public IStateRepository Local { get; }

    public IStateRepository SqlServer { get; }

    public StateRepositories(IEnumerable<IStateRepository> repositories)
    {
        Local = repositories.OfType<LocalRepository>().FirstOrDefault();
        SqlServer = repositories.OfType<DapperRepository>().FirstOrDefault();
    }
}

Inject different implementations that have same interface in multiple constructor parameters

1 Answers1