The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

C# Projects Workflow

Tool Grid

dotnet roslynator analyze

dotnet format

dotnet build

dotnet test

dotnet publish

dotnet watch run

dotnet restore

dotnet add package <name>

C# 12+ Features

Primary Constructors

SHOULD use primary constructors for dependency injection and simple initialization:

public class UserService(IUserRepository repository, ILogger<UserService> logger)
{
    public async Task<User?> GetByIdAsync(int id) => await repository.FindAsync(id);
}

Collection Expressions

SHOULD use collection expressions for collection initialization:

// Preferred
int[] numbers = [1, 2, 3, 4, 5];
List<string> names = ["Alice", "Bob", "Charlie"];

// Spread operator
int[] combined = [..firstArray, ..secondArray];

Raw String Literals

SHOULD use raw string literals for multi-line strings and strings containing quotes:

var json = """
    {
        "name": "Example",
        "value": 42
    }
    """;

File-Scoped Namespaces

MUST use file-scoped namespaces to reduce nesting:

namespace MyApp.Services;

public class MyService { }

.NET 8+ Patterns

Minimal APIs

SHOULD use minimal APIs for microservices and simple endpoints:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/api/users/{id}", async (int id, IUserService service) =>
    await service.GetByIdAsync(id) is User user
        ? Results.Ok(user)
        : Results.NotFound());

app.Run();

AOT Compilation

SHOULD design for AOT compatibility when targeting native deployment:

• MUST NOT use reflection-heavy patterns
• SHOULD use source generators instead of runtime reflection
• MUST use

  [JsonSerializable]

  for System.Text.Json

[JsonSerializable(typeof(User))]
[JsonSerializable(typeof(List<User>))]
internal partial class AppJsonContext : JsonSerializerContext { }

Keyed Services

MAY use keyed services for named dependency resolution:

builder.Services.AddKeyedSingleton<ICache, RedisCache>("redis");
builder.Services.AddKeyedSingleton<ICache, MemoryCache>("memory");

Naming Conventions

General Rules

GetUserAsync()

_userRepository

userName

MaxRetryCount

IUserService

TEntity

GetUserAsync()

MUST Follow

• MUST use

  I

  prefix for interfaces
• MUST use

  Async

  suffix for async methods
• MUST NOT use Hungarian notation
• MUST NOT use underscores in public identifiers

Nullable Reference Types

Configuration

MUST enable nullable reference types in all projects:

<PropertyGroup>
    <Nullable>enable</Nullable>
</PropertyGroup>

Usage Rules

• MUST annotate all reference types explicitly
• MUST handle null appropriately with null-conditional operators
• SHOULD use

  required

  keyword for required properties
• MUST NOT use

  !

  (null-forgiving operator) except when absolutely necessary

public class User
{
    public required string Name { get; init; }
    public string? Email { get; set; }
}

Async/Await Best Practices

Rules

• MUST use async all the way (no sync-over-async)
• MUST use

  ConfigureAwait(false)

  in library code
• MUST use

  CancellationToken

  for cancellable operations
• SHOULD prefer

  ValueTask

  for hot paths with frequent sync completion
• MUST NOT use

  async void

  except for event handlers

public async Task<User?> GetUserAsync(int id, CancellationToken ct = default)
{
    return await _repository.FindAsync(id, ct).ConfigureAwait(false);
}

Exception Handling

• MUST catch specific exceptions, not

  Exception

• SHOULD use

  when

  clause for conditional catches
• MUST NOT swallow exceptions silently

Dependency Injection

Rules

• MUST use constructor injection for required dependencies
• SHOULD use primary constructors for DI
• MUST NOT use service locator pattern
• MUST register services with appropriate lifetime

// Registration
builder.Services.AddScoped<IUserService, UserService>();
builder.Services.AddSingleton<ICacheService, CacheService>();
builder.Services.AddTransient<IEmailService, EmailService>();

Lifetime Guidelines

Record Types

DTOs and Value Objects

MUST use records for DTOs and immutable data:

public record UserDto(int Id, string Name, string? Email);

public record CreateUserRequest(string Name, string Email);

public record ApiResponse<T>(T Data, bool Success, string? Error = null);

Rules

• MUST use positional records for simple DTOs
• MAY use record classes with properties for complex objects
• SHOULD use

  with

  expressions for immutable updates

LINQ Best Practices

Method Syntax

SHOULD prefer method syntax over query syntax:

// Preferred
var adults = users
    .Where(u => u.Age >= 18)
    .OrderBy(u => u.Name)
    .Select(u => new UserDto(u.Id, u.Name, u.Email));

// Avoid query syntax for simple queries
var adults = from u in users
             where u.Age >= 18
             select u;

Performance

• MUST materialize queries when iterating multiple times
• SHOULD use

  Any()

  instead of

  Count() > 0

• SHOULD use

  FirstOrDefault()

  with predicate
• MUST NOT use LINQ in hot paths without benchmarking

Testing

Framework Options

dotnet test

dotnet test

dotnet test

xUnit Patterns (RECOMMENDED)

public class UserServiceTests
{
    private readonly Mock<IUserRepository> _mockRepo = new();
    private readonly UserService _sut;

    public UserServiceTests()
    {
        _sut = new UserService(_mockRepo.Object);
    }

    [Fact]
    public async Task GetByIdAsync_WhenUserExists_ReturnsUser()
    {
        // Arrange
        var expected = new User { Id = 1, Name = "Test" };
        _mockRepo.Setup(r => r.FindAsync(1, default))
            .ReturnsAsync(expected);

        // Act
        var result = await _sut.GetByIdAsync(1);

        // Assert
        Assert.Equal(expected, result);
    }

    [Theory]
    [InlineData(0)]
    [InlineData(-1)]
    public async Task GetByIdAsync_WhenIdInvalid_ThrowsArgumentException(int id)
    {
        await Assert.ThrowsAsync<ArgumentException>(() => _sut.GetByIdAsync(id));
    }
}

Rules

• MUST follow Arrange-Act-Assert pattern
• MUST use meaningful test names
• SHOULD use

  [Theory]

  for parameterized tests
• MUST mock external dependencies

Project Structure

RECOMMENDED Layout

MySolution/
├── src/
│   ├── MyApp.Api/
│   │   ├── Controllers/
│   │   ├── Endpoints/
│   │   └── Program.cs
│   ├── MyApp.Application/
│   │   ├── Services/
│   │   └── DTOs/
│   ├── MyApp.Domain/
│   │   ├── Entities/
│   │   └── Interfaces/
│   └── MyApp.Infrastructure/
│       ├── Data/
│       └── Services/
├── tests/
│   ├── MyApp.UnitTests/
│   └── MyApp.IntegrationTests/
├── Directory.Build.props
├── Directory.Packages.props
└── MySolution.sln

Directory.Build.props

SHOULD use centralized build configuration:

<Project>
    <PropertyGroup>
        <TargetFramework>net8.0</TargetFramework>
        <ImplicitUsings>enable</ImplicitUsings>
        <Nullable>enable</Nullable>
        <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
    </PropertyGroup>
</Project>

Error Handling

Result Pattern

SHOULD use Result pattern for expected failures:

public record Result<T>(T? Value, bool IsSuccess, string? Error = null)
{
    public static Result<T> Success(T value) => new(value, true);
    public static Result<T> Failure(string error) => new(default, false, error);
}

Exceptions

• MUST use exceptions for exceptional conditions only
• SHOULD create custom exceptions for domain errors
• MUST include relevant context in exception messages

Configuration

Options Pattern

MUST use Options pattern for configuration:

public class DatabaseOptions
{
    public const string SectionName = "Database";
    public required string ConnectionString { get; init; }
    public int MaxRetryCount { get; init; } = 3;
}

// Registration
builder.Services.Configure<DatabaseOptions>(
    builder.Configuration.GetSection(DatabaseOptions.SectionName));

Code Quality

Analyzers

SHOULD enable code analysis:

<PropertyGroup>
    <EnableNETAnalyzers>true</EnableNETAnalyzers>
    <AnalysisLevel>latest-recommended</AnalysisLevel>
</PropertyGroup>

EditorConfig

MUST include

.editorconfig