Resolving conditional dependencies autofac

6
votes

I am trying to resolve dependencies based on a condition. 

private static readonly Dictionary<string, Action<ContainerBuilder>> QRTypeDictionary = 
    new Dictionary<string, System.Action<ContainerBuilder>> () {
            { "REST" , (builder)=> builder
                                    .RegisterType<RestPublisher>()
                                    .As<Publisher>()},
            { "DB" , (builder)=> builder
                                    .RegisterType<DBPublisher>()
                                    .As<Publisher>()}
 }

I am just looking to make sure if this is the only way to resolve dependencies based on conditions. I have been using Ninject so far and am looking for something like the following: 

kernel.Bind<Publisher>()
      .To<DbPublisher>()
      .When(x => Defs.AppSettings.PublisherType == "DB")

Just want to make sure I am doing the right thing with Autofac

1
c#autofac
Is Defs.AppSettings.PublisherType a configuration value that needs an application restart to change, or can it change from time to time (between requests for instance)? - Steven

1 Answers

12
votes

I can see 3 solutions to achieve what you want.

  1. Using a lambda

    builder.RegisterType<DbPublisher>().AsSelf();
builder.RegisterType<RestPublisher>().AsSelf();

builder.Register(c => { 
    switch(Defs.AppSettings.PublisherType){
        case "DB":
            c.Resolve<DbPublisher>(); 
            break; 
        case "REST":
            c.Resolve<RestPublisher>(); 
            break; 
        default:
            throw new NotSupportedException(); 
    }
}).As<IPublisher>();

  2. Using named registration

    builder.RegisterType<DbPublisher>().Named<IPublisher>("DB");
builder.RegisterType<RestPublisher>().Named<IPublisher>("REST");

builder.Register(c => {
      var index = c.Resolve<IIndex<String, IPublisher>>(); 
      return index[Defs.AppSettings.PublisherType]
}.As<IPublisher>();

  3. Conditional registration

    if Defs.AppSettings.PublisherType is defined during registration process, you can simply conditionally register your dependency : 

    switch(Defs.AppSettings.PublisherType){
    case "DB":
        builder.RegisterType<DbPublisher>().As<IPublisher>();
        break; 
    case "REST":
        builder.RegisterType<RestPublisher>().As<IPublisher>(); 
        break; 
    default:
        throw new NotSupportedException(); 
}