dotnet

Security (Critical)

• Use [Authorize] attribute with policies
• Validate anti-forgery tokens for forms
• Use parameterized queries (EF Core does this by default)
• Don't log sensitive data
• Use HTTPS redirection middleware
• Store secrets in Azure Key Vault or environment variables
• Use User Secrets for local development
• Never commit secrets to source control
• Validate and sanitize all user input to prevent injection attacks
• Avoid storing sensitive data or security-relevant instructions in HTML comments

Dependency Injection

• Register services with appropriate lifetime:

- Singleton: stateless, thread-safe services

- Scoped: per-request services (DbContext, etc.)

- Transient: lightweight, stateless services

• Avoid captive dependencies (Singleton depending on Scoped)
• Use IOptions pattern for configuration

Async/Await

• Use async/await for I/O-bound operations (database, HTTP calls, file system)
• Always pass CancellationToken and respect it
• Avoid .Result or .Wait() (causes deadlocks)
• Use ConfigureAwait(false) in library code

Advanced Async Patterns

• Prefer ValueTask for hot paths that often complete synchronously

Controllers

• Keep controllers thin (delegate to services)
• Use [ApiController] attribute for automatic model validation
• Return ActionResult for type safety
• Use [ProducesResponseType] for API documentation
• Implement API versioning (URL, header, or query string)
• Use consistent versioning strategy across endpoints

Middleware

• Order matters: add middleware in correct sequence
• Authentication before Authorization
• Error handling middleware should be first (to catch all exceptions)
• Use app.UseExceptionHandler() for production error handling

Model Validation

• Use Data Annotations or FluentValidation
• Validate at API boundary, not deep in business logic
• Return 400 Bad Request for validation failures
• Include validation errors in response body

Entity Framework Core (Essential)

• Use AsNoTracking() for read-only queries
• Avoid N+1 queries (use Include() or projection)
• Use migrations for schema changes
• Don't expose entities directly (use DTOs)
• Manage DbContext lifetime properly (scoped per request)
• Use async methods for database operations

Advanced EF Core Patterns

• Use compiled queries for hot paths that execute frequently
• Use raw SQL via FromSqlInterpolated/ExecuteSqlInterpolated for complex queries while keeping parameters parameterized
• Define global query filters for concerns like soft deletes or multi-tenancy
• Consider splitting DbContexts by bounded context to keep models focused and reduce migration complexity

Logging and Exception Handling

• Use structured logging with ILogger
• Include correlation IDs for request tracing
• Log exceptions at appropriate levels (Error, Warning, Information)
• Use centralized exception handling middleware
• Don't catch exceptions unless you can handle them
• Include relevant context in log messages

Thread Safety

• Singleton services must be thread-safe
• Avoid mutable shared state in singletons
• Use lock, SemaphoreSlim, or ConcurrentDictionary for shared resources
• Be cautious with static fields

Testing

• Write unit tests for business logic
• Use in-memory providers for EF Core in tests
• Mock external dependencies with interfaces
• Test controller actions with integration tests
• Use WebApplicationFactory for integration testing