Issue
In this blog post I’ll describe a situation I encountered in one of my projects, where I had to access an interface that was registered as a scoped service from BackgroundService, which is singleton. In essence, I’ll describe a neat trick on how to access scoped service from singleton service.
In the Program.cs of this example web app we have our initialization of builder and method that adds example service in a pattern I really like, split by features, which also makes it more readable. In this case AddExampleFeature() can contain various service descriptors for a given feature of a web app.
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var builder = WebApplication.CreateBuilder(args);
builder.Services.AddExampleFeature()
Then we have our given IServiceCollection method that defines lifecycle of example service
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public static class IServiceCollectionExtension
{
public static IServiceCollection AddExampleFeature(this IServiceCollection services)
{
services.AddScoped<IRandomRepository, RandomRepository>();
return services;
}
}
If we would want to consume this given interface from BackgroundService which by design has a singleton lifecycle, we would run into an exception as scoped service cannot be consumed by singleton service. Application would thrown this exception:
InvalidOperationException: Cannot consume scoped service 'Random.Path.ToFile.RandomRepository' from singleton 'Random.Path.ToBackgroundService.ExampleBackgroundService'.
Solution
To circumvent this we can pass IServiceProvider in the BackgroundService constructor and create a new IServiceScope within BackgroundService to resolve scoped service.
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public class ExampleBackgroundService(
IServiceProvider provider)
: BackgroundService
{
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
using var scope = provider.CreateScope();
{
var randomRepository = scope.ServiceProvider.GetRequiredService<IRandomRepository>();
//do magic with your random repository
}
}
}
By utilizing the IServiceProvider extension method we can now play around with transient or scoped services within BackgroundService.
Thank you for reading
More on IServiceProvider here: https://learn.microsoft.com/en-us/dotnet/api/system.iserviceprovider?view=net-8.0 More on IServiceScope here: https://learn.microsoft.com/en-us/dotnet/api/microsoft.extensions.dependencyinjection.serviceproviderserviceextensions.createscope?view=net-8.0 More on DI and Lifecycles here: https://learn.microsoft.com/en-us/aspnet/core/fundamentals/dependency-injection?view=aspnetcore-8.0