dependency-injection-patterns

1# Dependency Injection Patterns
2 
3## When to Use This Skill
4 
5Use this skill when:
6- Organizing service registrations in ASP.NET Core applications
7- Avoiding massive Program.cs/Startup.cs files with hundreds of registrations
8- Making service configuration reusable between production and tests
9- Designing libraries that integrate with Microsoft.Extensions.DependencyInjection
10 
11## Reference Files
12 
13- [advanced-patterns.md](advanced-patterns.md): Testing with DI extensions, Akka.NET actor scope management, conditional/factory/keyed registration patterns
14 
15---
16 
17## The Problem
18 
19Without organization, Program.cs becomes unmanageable:
20 
21```csharp
22// BAD: 200+ lines of unorganized registrations
23var builder = WebApplication.CreateBuilder(args);
24 
25builder.Services.AddScoped<IUserRepository, UserRepository>();
26builder.Services.AddScoped<IOrderRepository, OrderRepository>();
27builder.Services.AddScoped<IProductRepository, ProductRepository>();
28builder.Services.AddScoped<IUserService, UserService>();
29// ... 150 more lines ...
30```
31 
32Problems: hard to find related registrations, no clear boundaries, can't reuse in tests, merge conflicts.
33 
34---
35 
36## The Solution: Extension Method Composition
37 
38Group related registrations into extension methods:
39 
40```csharp
41// GOOD: Clean, composable Program.cs
42var builder = WebApplication.CreateBuilder(args);
43 
44builder.Services
45    .AddUserServices()
46    .AddOrderServices()
47    .AddEmailServices()
48    .AddPaymentServices()
49    .AddValidators();
50 
51var app = builder.Build();
52…