# dependency-injection

Guides dependency injection patterns in .NET 10, covering service lifetimes, keyed services, Scrutor decorators, and captive dependency fixes.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 2800 installs · ★ 789
- Author: codewithmukesh
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/codewithmukesh/dotnet-claude-kit/tree/HEAD/skills/dependency-injection/SKILL.md
- Updated: 2026-08-07
- HTML: https://affpapa.org/en/nevibecode/skills/dependency-injection

## What it does

The skill establishes dependency injection rules for .NET 10 projects. Constructor injection is the default choice. Service locators and property injection are excluded entirely. To select between multiple implementations, it relies on .NET 8+ keyed services via `[FromKeyedServices]` and `GetRequiredKeyedService`.

It includes practical templates for the decorator pattern using Scrutor, assembly scanning by convention, and runtime selection using factory delegates. Capturing a scoped service like `AppDbContext` inside a singleton causes stale data and memory leaks, so the guide enforces `IServiceScopeFactory` for background operations.

For reviewing existing architectures, the skill suggests the `get_di_registrations` MCP tool. That tool checks lifetime mismatches and duplicate registrations in a single pass.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add codewithmukesh/dotnet-claude-kit --skill dependency-injection -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/dependency-injection/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/dependency-injection/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add codewithmukesh/dotnet-claude-kit --skill dependency-injection -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/dependency-injection/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add codewithmukesh/dotnet-claude-kit --skill dependency-injection -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/dependency-injection/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install codewithmukesh/dotnet-claude-kit dependency-injection
```

2. **Manually: put the files in place**
- File: `.github/skills/dependency-injection/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add codewithmukesh/dotnet-claude-kit --skill dependency-injection -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/codewithmukesh/dotnet-claude-kit --path skills/dependency-injection
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/dependency-injection/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add codewithmukesh/dotnet-claude-kit --skill dependency-injection -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/codewithmukesh/dotnet-claude-kit/tree/HEAD/skills/dependency-injection/SKILL.md

## When to use it
- configure keyed services for multiple implementations of an interface
- decorate existing services with logging using Scrutor
- resolve captive dependencies when scoped services are needed in singletons
- register application services automatically via assembly scanning
- bind strongly-typed configuration sections with AddOptions

## Example prompts
- Show me how to register keyed services for INotificationService in .NET 10
- Add a logging decorator to OrderService using Scrutor
- How do I safely resolve AppDbContext inside a singleton cache service?

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 92fb942d85b99612.

BEGIN THIRD-PARTY FILE 92fb942d85b99612
````text
---
name: dependency-injection
description: >
  Dependency injection patterns for .NET 10. Covers service lifetimes, keyed
  services, the decorator pattern, factory pattern, and common DI pitfalls.
  Load this skill when registering services, resolving lifetime issues, designing
  service composition, or when the user mentions "DI", "dependency injection",
  "service registration", "AddScoped", "AddTransient", "AddSingleton", "keyed
  services", "decorator", "Scrutor", "IServiceCollection", or "captive dependency".
---

# Dependency Injection

## Core Principles

1. **Constructor injection is the default** — Inject dependencies through the constructor (primary constructors make this clean). No service locator, no property injection.
2. **Match lifetimes carefully** — A singleton must never depend on a scoped or transient service. This is the most common DI bug.
3. **Register interfaces, resolve interfaces** — Register `services.AddScoped<IOrderService, OrderService>()`, not the concrete type.
4. **Keyed services for strategy pattern** — .NET 8+ keyed services replace manual factory patterns for selecting between implementations.

## Patterns

### Keyed Services (.NET 8+)

Use keyed services to register and resolve multiple implementations of the same interface.

```csharp
// Registration
builder.Services.AddKeyedScoped<INotificationService, EmailNotificationService>("email");
builder.Services.AddKeyedScoped<INotificationService, SmsNotificationService>("sms");
builder.Services.AddKeyedScoped<INotificationService, PushNotificationService>("push");

// Resolution via attribute
public class OrderHandler([FromKeyedServices("email")] INotificationService notifier)
{
    public async Task Handle(CreateOrder.Command command, CancellationToken ct)
    {
        // ... create order
        await notifier.SendAsync(notification, ct);
    }
}

// Resolution via IServiceProvider
public class NotificationRouter(IServiceProvider provider)
{
    public INotificationService GetService(string channel)
    {
        return provider.GetRequiredKeyedService<INotificationService>(channel);
    }
}
```

### Decorator Pattern

```csharp
// Base service
public interface IOrderService
{
    Task<Result<Order>> CreateAsync(CreateOrderRequest request, CancellationToken ct);
}

public class OrderService(AppDbContext db, TimeProvider clock) : IOrderService
{
    public async Task<Result<Order>> CreateAsync(CreateOrderRequest request, CancellationToken ct)
    {
        var order = Order.Create(request, clock.GetUtcNow());
        db.Orders.Add(order);
        await db.SaveChangesAsync(ct);
        return Result.Success(order);
    }
}
````
END THIRD-PARTY FILE 92fb942d85b99612

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