refactor-dotnet_skill

Overview

This skill refactors ASP.NET Core and C# code to improve maintainability, readability, and alignment with modern .NET practices. It transforms fat controllers, duplicated logic, and legacy patterns into clean, testable code using C# 12 features, SOLID principles, and Clean Architecture. The result is smaller, focused classes, better dependency injection, and idiomatic async/await usage.

How this skill works

The skill inspects controllers, services, and data access layers to locate anti-patterns such as service locators, captive dependencies, and duplicated logic. It rewrites code to apply primary constructors, collection expressions, records, nullable annotations, and pattern matching while introducing well-scoped services, Result types, and proper EF Core usage (No-Tracking, projection, eager loading). It also suggests or implements dependency lifetimes, options pattern, and middleware improvements to align with .NET 8 practices.

When to use it

• You have fat controllers containing business logic that should be moved to services.
• There is duplicated code across controllers, services, or repository layers.
• You’re upgrading to C# 12/.NET 8 and want to adopt modern language features safely.
• A singleton depends on scoped services or you observe captive dependency/service locator anti-patterns.
• Database queries cause N+1 issues or return too much data (no projection).

Best practices

• Prefer constructor injection and explicit lifetimes; avoid IServiceProvider in business code.
• Keep controllers skinny: validate input, call services, return HTTP results.
• Extract repeated logic to services, extension methods, or small helpers to satisfy DRY.
• Adopt primary constructors, records for DTOs, and required/init-only properties for immutable models.
• Use No-Tracking for read queries, Include/AsSplitQuery to prevent N+1, and projection to DTOs for performance.

Example use cases

• Refactor an OrdersController that mixes validation, mapping, and persistence into a thin controller plus OrderService using primary constructors.
• Replace duplicated input validation across endpoints with a shared request validator and Result<T> return pattern.
• Migrate legacy repository code to EF Core projections with AsNoTracking and fixed eager loading to eliminate N+1 queries.
• Convert background singleton that needs DbContext to use IServiceScopeFactory to avoid captive dependency.
• Upgrade DTOs to record types, introduce global usings, and apply collection expressions to simplify collection construction.