OverridableDependencyInjection 1.0.5

OverridableDependencyInjection

A small extension for Microsoft.Extensions.DependencyInjection that lets you override registered services inside a specific scope without changing the root container configuration.

This is useful for tests, request-specific behavior, and temporary substitutions when you need a different implementation for a single unit of work.

Why use it?

• Override a service only for one IServiceScope
• Keep the original registrations intact for the rest of the app
• Works with regular services, keyed services, and open generic interfaces
• Very lightweight integration with ServiceCollection

Installation

dotnet add package OverridableDependencyInjection

Quick start

using Microsoft.Extensions.DependencyInjection;

var provider = new ServiceCollection()
    .AddTransient<IExampleService1, ExampleService1A>()
    .AddTransient<IExampleService2, ExampleService2>()

    // Mark which services may be overridden
    .AddOverridability(typeof(IExampleService1))
    .BuildServiceProvider();

using (var scope = provider.CreateScope())
{
    scope.Override<IExampleService1, ExampleService1B>();

    var service = scope.ServiceProvider.GetRequiredService<IExampleService1>();
    Console.WriteLine(service is ExampleService1B); // True
}

Basic API

Register overridable services

var services = new ServiceCollection();

services.AddTransient<IWeatherService, WeatherService>();
services.AddTransient<IAuditService, AuditService>();
services.AddOverridability(typeof(IWeatherService), typeof(IAuditService));

You can also do it with generics:

services.AddOverridability<IWeatherService>();

Override inside a scope

using var scope = provider.CreateScope();

scope.Override<IWeatherService, FakeWeatherService>();

You can also override by instance or factory:

scope.Override<IWeatherService>(new FakeWeatherService());
scope.Override<IWeatherService>(_ => new FakeWeatherService());

Override a service type directly

scope.Override(typeof(IWeatherService), typeof(FakeWeatherService));

Open generic support

This library also supports open generic interfaces:

var provider = new ServiceCollection()
    .AddTransient(typeof(IRepository<>), typeof(Repository<>))
    .AddOverridability(typeof(IRepository<>))
    .BuildServiceProvider();

using var scope = provider.CreateScope();
scope.Override(typeof(IRepository<>), typeof(FakeRepository<>));

Keyed services

Keyed overrides are supported as well:

var provider = new ServiceCollection()
    .AddKeyedTransient<IExampleService, ExampleServiceA>("primary")
    .AddOverridability(typeof(IExampleService))
    .BuildServiceProvider();

using var scope = provider.CreateScope();
scope.OverrideKeyed<IExampleService, ExampleServiceB>("primary");

Important behavior

• AddOverridability(...) must be called before BuildServiceProvider().
• Overrides are scoped to the lifetime of the IServiceScope.
• The original registration remains available outside that scope.
• Only service types registered with AddOverridability can be overridden.

Example application

The repository includes a working demo app:

• ExampleApp/Program.cs

License

MIT