ChildServiceProvider 1.0.0

ChildServiceProvider

A small, high‑performance extension for Microsoft.Extensions.DependencyInjection that lets you create child service providers on top of an existing ServiceProvider, overriding or extending registrations while still sharing the same dependency graph.

• Zero API magic: built on top of IServiceCollection, ServiceProvider, and scopes you already know.
• Child‑first resolution: child registrations override parent ones (including open generics and keyed services).
• Scope‑aware: scoped services and lifetimes behave exactly as with the default DI container.
• Focused: no configuration system, no modules, just child containers.

Getting started

Installation

Add the package from NuGet (package name pending):

dotnet add package ChildServiceProvider

Basic usage

Start with a regular parent ServiceCollection and build a standard ServiceProvider. Then create a ChildServiceCollection that inherits those registrations and build a ChildServiceProvider from it.

using Microsoft.Extensions.DependencyInjection;

var parentServices = new ServiceCollection();
parentServices.AddSingleton<IMyService, ParentService>();

var parentProvider = parentServices.BuildServiceProvider();

// Create child collection based on the parent registrations
var childServices = parentServices.CreateChildServiceCollection();

// Override or add services in the child
childServices.AddSingleton<IMyService, ChildService>();
childServices.AddSingleton<IOtherService, OtherService>();

// Build the child provider
var childProvider = childServices.BuildChildServiceProvider(parentProvider);

// Resolves ChildService from the child provider
var service = childProvider.GetRequiredService<IMyService>();

// Still resolves ParentService from the parent provider
var parentService = parentProvider.GetRequiredService<IMyService>();

Key points:

• Parent registrations are visible from the child unless overridden.
• Child registrations never leak back into the parent provider.
• Transient, scoped and singleton lifetimes behave the same as in the default container.

Concepts

IChildServiceCollection

IChildServiceCollection is a view over two collections:

• ParentServices: the original parent IServiceCollection.
• ChildServices: the additional/overriding registrations for the child.

You usually create it from an existing IServiceCollection:

IServiceCollection parentServices = new ServiceCollection();
// ... configure parent ...

IChildServiceCollection childServices = parentServices.CreateChildServiceCollection();

ChildServiceProvider

ChildServiceProvider is an IServiceProvider, IKeyedServiceProvider, and IServiceScopeFactory that delegates to:

• the parent provider for services not overridden in the child; and
• the inner provider built from the child collection for overridden registrations.

Resolution rules:

• Closed types: if a service type is registered in the child, it wins over the parent.
• Open generics: if the child registers an open generic, it overrides parent closed and open generics for that service type.
• Keyed services: keyed registrations are treated independently per key; child keyed registrations override parent keyed ones with the same key.

Scopes

ChildServiceProvider fully supports scoping:

• CreateScope() creates a new scope on both the parent and inner providers.
• Scoped services resolved from the child behave as in the default container.
• Cross‑resolution works: a service from the parent can depend on a service registered only in the child and vice versa.

Example:

using var scope = childProvider.CreateScope();
var scoped = scope.ServiceProvider.GetRequiredService<IScopedService>();

Keyed services

On .NET 8+ with the new keyed services APIs, ChildServiceProvider implements IKeyedServiceProvider and understands keys during resolution.

var services = new ServiceCollection();
services.AddKeyedSingleton<IMyService>("parent", (sp, _) => new ParentService());

var parentProvider = services.BuildServiceProvider();
var child = services.CreateChildServiceCollection();
child.AddKeyedSingleton<IMyService>("parent", (sp, _) => new ChildService());

var childProvider = child.BuildChildServiceProvider(parentProvider);

var keyed = ((IKeyedServiceProvider)childProvider)
    .GetRequiredKeyedService(typeof(IMyService), "parent");

In this example, the child keyed registration for key "parent" overrides the parent one.

Benchmarks

This repository includes a small BenchmarkDotNet project under benchmarks/ comparing:

• default ServiceProvider resolution,
• ChildServiceProvider with all registrations in the parent,
• ChildServiceProvider with overrides in the child,
• mixed scenarios where dependencies live in parent/child.

To run the benchmarks:

cd benchmarks
dotnet run -c Release

Development

Requirements

• .NET SDK 8.0 or later (project targets net8.0, net9.0, net10.0).

Build and test

From the repository root:

dotnet build

dotnet test

Project structure

• src/ – main library (ChildServiceProvider, ChildServiceCollection, resolution helpers).
• tests/ – xUnit test suite covering resolution, scoping, disposal and generics.
• benchmarks/ – BenchmarkDotNet project to measure performance.

Usage notes

• Use a ChildServiceProvider when you need per‑tenant or per‑feature overrides without duplicating the entire registration graph.
• Avoid deep hierarchies of child providers; a small number of layers keeps reasoning about lifetimes simpler.
• When debugging resolution, it can help to check whether a service is present in the child or only in the parent collection.