Can I inititialize WebHostBuilder with and existing container?

[hellfirehd]

The call to .UseStructureMap() expects nothing or a Registry. Either way it creates a brand new container.

I would prefer to use an existing container with cross cutting services that the entire application uses, not just WebHost.

This could be done if there was a .UseStructureMap(IContainer) overload. Is there any interest in this? Or is it a bad idea and if so, why?

[khellang]

The whole reason there is a UseStructureMap method is for the ASP.NET Core host to automatically wire up the container. This means also calling Startup.ConfigureContainer with the specific TContainerBuilder, before the container is built. In this case, it would call it with an IContainer instance, which makes it a bit weird when you want to keep configuring the registry. I'll have to think a bit about this one.

[hellfirehd]

I understand that. In my app ASP.NET is only a small component. It's essentially only providing a Web UI/API to a long running daemon and database. The daemon relies heavily on IoC/DI and needs to share services with the ASP.NET bit.

In theory I could take the Deluge approach with a deluge.web and a deluge.daemon but I'd really rather have it all self contained in a single process that starts and stops together like NZBGet or Sonarr.

See where I'm going with this?

[jeremydmiller]

@khellang @dougkwilson We suddenly need this feature at work for hybrid aspnet core/service bus apps. One of us will get a PR in for this one this week.

[khellang]

There's already a PR at #24 (although that seems to have drifted pretty far out of scope by now). The question I have is; how valuable is this? Is this just a way to pass the container into Startup? The container is already built by the time it's passed into ConfigureContainer. What are you going to do with it?

[jeremydmiller]

One way or another, we just need an easy recipe to build a new ASP.Net Core app by handing it an existing StructureMap Container. The immediate use case for us is an application that uses both a service bus framework and ASP.Net Core, and both need to add their own registrations to the StructureMap Container.

I think this is valuable. I was actually under the impression that we already had this before last week.

[khellang]

Oh, I definitely think passing a pre-configure container is valuable, but I'm just not sure this is the way to go. If we bring this in as-is, it could be very confusing for the user; depending on which overload of UseStructureMap you call (the one taking a Registry or IContainer), the ASP.NET Core hosting layer will look for a different ConfigureContainer overload. This might not be obvious for the end user. Maybe we can rectify this with documentation?

[jeremydmiller]

Instead of an overload of UseStructureMap, what if it's semantically different like UseExistingStructureMapContainer(IContainer)? I do agree on the potential user confusion. We had similar issues with that w/ fubumvc.

[hellfirehd]

Semantically different works for me. Would child or nested containers be appropriate?

[jeremydmiller]

Child containers, maybe, nested no. If you were sharing the container w/ some other piece of infrastructure but needed to override some things, I guess a Child container would work.

[joelweiss]

So is there currently a way to use an existing container?

[zordark]

You can pass initialized container to Startup class directly.

  public class Startup : IStartup {
        private IContainer _container;
        public Startup(IConfiguration configuration, IContainer container)
        {
            Configuration = configuration;
            _container = container;
       }

        public IConfiguration Configuration { get; }

        public IServiceProvider ConfigureServices(IServiceCollection services)
        {
            // Register additional stuff
            // .....

            // populate the container using the service collection.
            _container.Populate(services);

            return _container.GetInstance<IServiceProvider>();
        }
        public void Configure(IApplicationBuilder app)
        {
             //do additional work 
        }
    }

After that you should instantiate Startup and build host

var container = new Container();
// configure container
// .......

var configurationBuilder = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddJsonFile("appsettings.json");

var configuration = configurationBuilder.Build();

var startup = new Startup(configuration, container);

var builder = WebHost.CreateDefaultBuilder()
    .UseSetting(WebHostDefaults.ApplicationKey, typeof(Startup).Assembly.GetName().Name)
    .ConfigureServices(services => services.AddSingleton<IStartup>(startup))
    .UseKestrel(options =>
    {
        options.Listen(IPAddress.Loopback, 1113);
    });

var host = builder.Build();

You can read this article for some details.

But be careful with child container, I don't know why, but some dependencies (e.g. registered as singleton or open generic) cannot be resolved, when using child container.

This code will fail

var container = new Container();

var configurationBuilder = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddJsonFile("appsettings.json");

var configuration = configurationBuilder.Build();

var startup = new Startup(configuration, container.CreateChildContainer());

var builder = WebHost.CreateDefaultBuilder()
    .UseSetting(WebHostDefaults.ApplicationKey, typeof(Startup).Assembly.GetName().Name)
    .ConfigureServices(services => services.AddSingleton<IStartup>(startup))
    .UseKestrel(options =>
    {
        options.Listen(IPAddress.Loopback, 1113);
    });

var host = builder.Build();

Above code will fail, when try to resolve IServer instance within WebHost class, with exception
StructureMap.StructureMapConfigurationException : No default Instance is registered and cannot be automatically determined for type 'IOptions<KestrelServerOptions>'

[RubenDelange]

I'm also interested in a way to use an existing container. Our solution has console apps, Windows services, web apps that all use the same logic to initialize the container.
Is there a good example to achieve this with ASP.NET Core 2.1 ?

[dazinator]

@zordark

Above code will fail, when try to resolve IServer instance within WebHost class, with exception
StructureMap.StructureMapConfigurationException : No default Instance is registered and cannot be automatically determined for type 'IOptions'

I am also having a problem with IOptions<T>. Perhaps this is related to #43

I have submitted a PR with a failing test case to demonstrate the issue, but I haven't been able to fix it.