How to validate all registered types in ASP.NET Core DI? - asp.net-core

Question

I want to check that the type registrations I established in Startup.cs are all valid at runtime (either when starting up the service or as part of a test suite). There's a feature like this in Lamar and other containers.

Answer 1

ASP.NET Core 3.x actually introduced a feature for scope and provider validation. Both of these are useful in different contexts (see the below post and sample code).
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseStartup<Startup>();
})
.UseDefaultServiceProvider((context, options) =>
{
options.ValidateScopes = context.HostingEnvironment.IsDevelopment();
options.ValidateOnBuild = true;
});
https://andrewlock.net/new-in-asp-net-core-3-service-provider-validation/

Answer 2

You can iterate the services that you want to validate, and try to initialize a service with GetRequiredService<T>. It will throw an exception if there is something wrong. More info on
https://learn.microsoft.com/en-us/dotnet/api/microsoft.extensions.dependencyinjection.serviceproviderserviceextensions.getrequiredservice?view=aspnetcore-2.2

Answer 3

The IServiceCollection is actually enumerable over ServiceDescriptor which contains type information on the registered service and implementation. The service collection isn't usually registered, but it should be possible to capture both the service collection and service provider in a hosted service.
Startup.cs
public void ConfigureServices(IServiceCollection services)
{
services.AddServicesValidation();
}
The right extension method can capture the services collection without actually registering it (which feels "safer").
public static class ValidateServicesExtensions
{
public static IServiceCollection AddServicesValidation(this IServiceCollection services)
{
services.AddHostedService<ValidateServices>(provider => new ValidateServices(services, provider));
return services;
}
}
Now, the hosted service can iterate over the registered services & implementations. Although, this code bombs on the first generic IOptions<TOption>, but I'm sure we can figure something out?
ValidateServices.cs
public class ValidateServices : BackgroundService
{
private readonly IServiceCollection services;
private readonly IServiceProvider provider;
public ValidateServices(
IServiceCollection services,
IServiceProvider provider
)
{
this.services = services;
this.provider = provider;
}
protected override Task ExecuteAsync(CancellationToken stoppingToken)
{
using var scope = provider.CreateScope();
foreach (var service in services)
{
_ = scope.ServiceProvider.GetRequiredService(service.ServiceType);
}
return Task.CompletedTask;
}
}