C# Best Practices

C# Best Practices

Priority: P1 (OPERATIONAL)

Idiomatic patterns for clean, maintainable C# code.

Implementation Guidelines

• Naming Conventions:
  • PascalCase: Types, methods, properties, events, namespaces
  • camelCase: Parameters, local variables
  • _camelCase: Private fields
  • IPascalCase: Interfaces (prefix with I)
  • TPascalCase: Type parameters (prefix with T)
• Project Structure: Clean/Onion architecture. Feature folders over layer folders.
• Dependency Injection: Constructor injection only. Register in IServiceCollection.
• Logging: ILogger<T> with structured logging. Use appropriate log levels.
• Configuration: IOptions<T> pattern with validation. Never hardcode settings.
• File Organization: One type per file. Use global using for common namespaces.
• Immutability: Prefer readonly, init, record for data integrity.
• Expression-bodied Members: Use for simple single-line methods/properties.

Anti-Patterns

• No static services: Use DI instead of static class ServiceHelper.
• No service locator: Avoid IServiceProvider.GetService() in business logic.
• No new() for dependencies: Inject via constructor.
• No magic strings: Use nameof(), constants, or configuration.
• No God classes: Split large classes by responsibility.
• No regions: Use partial classes or extract types instead.

Code

// Proper DI registration
public static class ServiceCollectionExtensions
{
    public static IServiceCollection AddApplicationServices(this IServiceCollection services)
    {
        services.AddScoped<IUserService, UserService>();
        services.AddScoped<IOrderService, OrderService>();

        services.AddOptions<EmailSettings>()
            .BindConfiguration("Email")
            .ValidateDataAnnotations()
            .ValidateOnStart();

        return services;
    }
}

// Structured logging with semantic names
public class OrderService(IOrderRepository repo, ILogger<OrderService> logger)
{
    public async Task<Order?> GetOrderAsync(int orderId, CancellationToken ct)
    {
        logger.LogDebug("Fetching order {OrderId}", orderId);

        var order = await repo.GetByIdAsync(orderId, ct);

        if (order is null)
            logger.LogWarning("Order {OrderId} not found", orderId);

        return order;
    }
}

// Options pattern with validation
public class EmailSettings
{
    public const string SectionName = "Email";

    [Required]
    public string SmtpHost { get; init; } = string.Empty;

    [Range(1, 65535)]
    public int SmtpPort { get; init; } = 587;

    [Required, EmailAddress]
    public string FromAddress { get; init; } = string.Empty;
}

Reference & Examples

For project structure templates and DI patterns: See references/REFERENCE.md.

Related Topics

language | security | tooling