┌─────────────────────────────────────────────────────────────┐
│                        API Layer                            │
│  Controllers, Middleware, Request/Response DTOs             │
├─────────────────────────────────────────────────────────────┤
│                   Infrastructure Layer                       │
│  EF Core, Repositories, External Services, Authentication   │
├─────────────────────────────────────────────────────────────┤
│                    Application Layer                         │
│  Commands, Queries, Handlers, Validators, DTOs              │
├─────────────────────────────────────────────────────────────┤
│                      Domain Layer                            │
│  Entities, Value Objects, Domain Events, Interfaces         │
└─────────────────────────────────────────────────────────────┘

Dependency Rule: Dependencies point inward. Domain has no dependencies. Application depends only on Domain. Infrastructure implements interfaces from Domain/Application.

Quick Reference

Task	Command/Action
Create solution	`dotnet new sln -n {SolutionName}`
Create Domain project	`dotnet new classlib -n {name}.domain`
Create Application project	`dotnet new classlib -n {name}.application`
Create Infrastructure project	`dotnet new classlib -n {name}.infrastructure`
Create API project	`dotnet new webapi -n {name}.api`
Add project to solution	`dotnet sln add src/{project}/{project}.csproj`
Add project reference	`dotnet add reference ../other/other.csproj`

Project Structure

{SolutionName}/
├── src/
│   ├── {name}.domain/
│   │   ├── Abstractions/
│   │   │   ├── Entity.cs
│   │   │   ├── IDomainEvent.cs
│   │   │   ├── IUnitOfWork.cs
│   │   │   └── Result.cs
│   │   ├── {Aggregate}/
│   │   │   ├── {Entity}.cs
│   │   │   ├── {Entity}Errors.cs
│   │   │   ├── I{Entity}Repository.cs
│   │   │   ├── ValueObjects/
│   │   │   └── Events/
│   │   └── {name}.domain.csproj
│   │
│   ├── {name}.application/
│   │   ├── Abstractions/
│   │   │   ├── Behaviors/
│   │   │   │   ├── LoggingBehavior.cs
│   │   │   │   └── ValidationBehavior.cs
│   │   │   ├── Messaging/
│   │   │   │   ├── ICommand.cs
│   │   │   │   ├── ICommandHandler.cs
│   │   │   │   ├── IQuery.cs
│   │   │   │   └── IQueryHandler.cs
│   │   │   ├── Authentication/
│   │   │   ├── Clock/
│   │   │   └── Data/
│   │   ├── {Feature}/
│   │   │   ├── Create{Entity}/
│   │   │   ├── Update{Entity}/
│   │   │   ├── Delete{Entity}/
│   │   │   └── Get{Entity}/
│   │   ├── DependencyInjection.cs
│   │   └── {name}.application.csproj
│   │
│   ├── {name}.infrastructure/
│   │   ├── Authentication/
│   │   ├── Authorization/
│   │   ├── Clock/
│   │   ├── Configurations/
│   │   ├── Repositories/
│   │   ├── Outbox/
│   │   ├── ApplicationDbContext.cs
│   │   ├── DependencyInjection.cs
│   │   └── {name}.infrastructure.csproj
│   │
│   └── {name}.api/
│       ├── Controllers/
│       ├── Middleware/
│       ├── Extensions/
│       ├── Program.cs
│       ├── appsettings.json
│       └── {name}.api.csproj
│
├── tests/
│   ├── {name}.domain.tests/
│   ├── {name}.application.tests/
│   └── {name}.api.tests/
│
└── {SolutionName}.sln

Step 1: Create Solution and Projects

# Create solution
dotnet new sln -n {SolutionName}

# Create projects
dotnet new classlib -n {name}.domain -o src/{name}.domain
dotnet new classlib -n {name}.application -o src/{name}.application
dotnet new classlib -n {name}.infrastructure -o src/{name}.infrastructure
dotnet new webapi -n {name}.api -o src/{name}.api

# Add projects to solution
dotnet sln add src/{name}.domain/{name}.domain.csproj
dotnet sln add src/{name}.application/{name}.application.csproj
dotnet sln add src/{name}.infrastructure/{name}.infrastructure.csproj
dotnet sln add src/{name}.api/{name}.api.csproj

# Add project references
cd src/{name}.application
dotnet add reference ../{name}.domain/{name}.domain.csproj

cd ../{name}.infrastructure
dotnet add reference ../{name}.domain/{name}.domain.csproj
dotnet add reference ../{name}.application/{name}.application.csproj

cd ../{name}.api
dotnet add reference ../{name}.application/{name}.application.csproj
dotnet add reference ../{name}.infrastructure/{name}.infrastructure.csproj

Step 2: Domain Layer Setup

Entity Base Class

// src/{name}.domain/Abstractions/Entity.cs
namespace {name}.domain.abstractions;

public abstract class Entity
{
    private readonly List<IDomainEvent> _domainEvents = new();

    protected Entity(Guid id)
    {
        Id = id;
    }

    protected Entity() { } // EF Core

    public Guid Id { get; init; }

    public IReadOnlyList<IDomainEvent> GetDomainEvents() => _domainEvents.ToList();

    public void ClearDomainEvents() => _domainEvents.Clear();

    protected void RaiseDomainEvent(IDomainEvent domainEvent) => _domainEvents.Add(domainEvent);
}

Domain Event Interface

// src/{name}.domain/Abstractions/IDomainEvent.cs
using MediatR;

namespace {name}.domain.abstractions;

public interface IDomainEvent : INotification
{
}

Unit of Work Interface

// src/{name}.domain/Abstractions/IUnitOfWork.cs
namespace {name}.domain.abstractions;

public interface IUnitOfWork
{
    Task<int> SaveChangesAsync(CancellationToken cancellationToken = default);
}

Result Pattern (see result-pattern skill for full implementation)

// src/{name}.domain/Abstractions/Result.cs
namespace {name}.domain.abstractions;

public class Result
{
    protected Result(bool isSuccess, Error error)
    {
        if (isSuccess && error != Error.None)
            throw new InvalidOperationException();
        if (!isSuccess && error == Error.None)
            throw new InvalidOperationException();

        IsSuccess = isSuccess;
        Error = error;
    }

    public bool IsSuccess { get; }
    public bool IsFailure => !IsSuccess;
    public Error Error { get; }

    public static Result Success() => new(true, Error.None);
    public static Result Failure(Error error) => new(false, error);
    public static Result<TValue> Success<TValue>(TValue value) => new(value, true, Error.None);
    public static Result<TValue> Failure<TValue>(Error error) => new(default, false, error);
}

public class Result<TValue> : Result
{
    private readonly TValue? _value;

    protected internal Result(TValue? value, bool isSuccess, Error error)
        : base(isSuccess, error)
    {
        _value = value;
    }

    public TValue Value => IsSuccess
        ? _value!
        : throw new InvalidOperationException("Cannot access value of a failed result");

    public static implicit operator Result<TValue>(TValue? value) =>
        value is not null ? Success(value) : Failure<TValue>(Error.NullValue);
}

public record Error(string Code, string Description)
{
    public static readonly Error None = new(string.Empty, string.Empty);
    public static readonly Error NullValue = new("Error.NullValue", "A null value was provided");
}

Step 3: Application Layer Setup

Package References

<!-- {name}.application.csproj -->
<ItemGroup>
    <PackageReference Include="FluentValidation" Version="11.*" />
    <PackageReference Include="FluentValidation.DependencyInjectionExtensions" Version="11.*" />
    <PackageReference Include="MediatR" Version="12.*" />
    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="8.*" />
</ItemGroup>

CQRS Abstractions

// src/{name}.application/Abstractions/Messaging/ICommand.cs
using MediatR;
using {name}.domain.abstractions;

namespace {name}.application.abstractions.messaging;

public interface ICommand : IRequest<Result> { }

public interface ICommand<TResponse> : IRequest<Result<TResponse>> { }

// src/{name}.application/Abstractions/Messaging/ICommandHandler.cs
using MediatR;
using {name}.domain.abstractions;

namespace {name}.application.abstractions.messaging;

public interface ICommandHandler<TCommand> : IRequestHandler<TCommand, Result>
    where TCommand : ICommand { }

public interface ICommandHandler<TCommand, TResponse> : IRequestHandler<TCommand, Result<TResponse>>
    where TCommand : ICommand<TResponse> { }

// src/{name}.application/Abstractions/Messaging/IQuery.cs
using MediatR;
using {name}.domain.abstractions;

namespace {name}.application.abstractions.messaging;

public interface IQuery<TResponse> : IRequest<Result<TResponse>> { }

// src/{name}.application/Abstractions/Messaging/IQueryHandler.cs
using MediatR;
using {name}.domain.abstractions;

namespace {name}.application.abstractions.messaging;

public interface IQueryHandler<TQuery, TResponse> : IRequestHandler<TQuery, Result<TResponse>>
    where TQuery : IQuery<TResponse> { }

Dependency Injection

// src/{name}.application/DependencyInjection.cs
using FluentValidation;
using Microsoft.Extensions.DependencyInjection;
using {name}.application.abstractions.behaviors;

namespace {name}.application;

public static class DependencyInjection
{
    public static IServiceCollection AddApplication(this IServiceCollection services)
    {
        services.AddMediatR(configuration =>
        {
            configuration.RegisterServicesFromAssembly(typeof(DependencyInjection).Assembly);
            configuration.AddOpenBehavior(typeof(LoggingBehavior<,>));
            configuration.AddOpenBehavior(typeof(ValidationBehavior<,>));
        });

        services.AddValidatorsFromAssembly(typeof(DependencyInjection).Assembly);

        return services;
    }
}

Step 4: Infrastructure Layer Setup

Package References

<!-- {name}.infrastructure.csproj -->
<ItemGroup>
    <PackageReference Include="Dapper" Version="2.*" />
    <PackageReference Include="EFCore.NamingConventions" Version="8.*" />
    <PackageReference Include="Microsoft.AspNetCore.Authentication.JwtBearer" Version="8.*" />
    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="8.*" />
    <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="8.*" />
    <PackageReference Include="Quartz.Extensions.Hosting" Version="3.*" />
</ItemGroup>

Application DbContext

// src/{name}.infrastructure/ApplicationDbContext.cs
using Microsoft.EntityFrameworkCore;
using {name}.application.abstractions.clock;
using {name}.domain.abstractions;

namespace {name}.infrastructure;

public sealed class ApplicationDbContext : DbContext, IUnitOfWork
{
    private readonly IDateTimeProvider _dateTimeProvider;

    public ApplicationDbContext(
        DbContextOptions<ApplicationDbContext> options,
        IDateTimeProvider dateTimeProvider)
        : base(options)
    {
        _dateTimeProvider = dateTimeProvider;
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.ApplyConfigurationsFromAssembly(typeof(ApplicationDbContext).Assembly);
        base.OnModelCreating(modelBuilder);
    }

    public override async Task<int> SaveChangesAsync(CancellationToken cancellationToken = default)
    {
        // Add domain events to outbox before saving
        AddDomainEventsAsOutboxMessages();
        return await base.SaveChangesAsync(cancellationToken);
    }

    private void AddDomainEventsAsOutboxMessages()
    {
        // See outbox-pattern skill for implementation
    }
}

Dependency Injection

// src/{name}.infrastructure/DependencyInjection.cs
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using {name}.application.abstractions.clock;
using {name}.application.abstractions.data;
using {name}.domain.abstractions;
using {name}.infrastructure.clock;

namespace {name}.infrastructure;

public static class DependencyInjection
{
    public static IServiceCollection AddInfrastructure(
        this IServiceCollection services,
        IConfiguration configuration)
    {
        services.AddTransient<IDateTimeProvider, DateTimeProvider>();

        AddPersistence(services, configuration);
        AddAuthentication(services, configuration);
        AddAuthorization(services);
        AddHealthChecks(services, configuration);

        return services;
    }

    private static void AddPersistence(IServiceCollection services, IConfiguration configuration)
    {
        var connectionString = configuration.GetConnectionString("Database")
            ?? throw new ArgumentNullException(nameof(configuration));

        services.AddDbContext<ApplicationDbContext>(options =>
        {
            options.UseNpgsql(connectionString)
                   .UseSnakeCaseNamingConvention();
        });

        services.AddScoped<IUnitOfWork>(sp => sp.GetRequiredService<ApplicationDbContext>());

        services.AddSingleton<ISqlConnectionFactory>(_ => new SqlConnectionFactory(connectionString));

        // Register repositories here
        // services.AddScoped<I{Entity}Repository, {Entity}Repository>();
    }

    private static void AddAuthentication(IServiceCollection services, IConfiguration configuration)
    {
        // See jwt-authentication skill
    }

    private static void AddAuthorization(IServiceCollection services)
    {
        // See permission-authorization skill
    }

    private static void AddHealthChecks(IServiceCollection services, IConfiguration configuration)
    {
        services.AddHealthChecks()
            .AddNpgSql(configuration.GetConnectionString("Database")!);
    }
}

Step 5: API Layer Setup

Program.cs

// src/{name}.api/Program.cs
using HealthChecks.UI.Client;
using Microsoft.AspNetCore.Diagnostics.HealthChecks;
using Serilog;
using {name}.application;
using {name}.infrastructure;

var builder = WebApplication.CreateBuilder(args);

builder.Host.UseSerilog((context, configuration) =>
    configuration.ReadFrom.Configuration(context.Configuration));

builder.Services.AddControllers();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

builder.Services.AddApplication();
builder.Services.AddInfrastructure(builder.Configuration);

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();
app.UseSerilogRequestLogging();
app.UseAuthentication();
app.UseAuthorization();
app.MapControllers();
app.MapHealthChecks("health", new HealthCheckOptions
{
    ResponseWriter = UIResponseWriter.WriteHealthCheckUIResponse
});

app.Run();

appsettings.json

{
  "ConnectionStrings": {
    "Database": "Host=localhost;Port=5432;Database={name}-db;Username=postgres;Password=postgres"
  },
  "Serilog": {
    "Using": ["Serilog.Sinks.Console"],
    "MinimumLevel": {
      "Default": "Information",
      "Override": {
        "Microsoft": "Warning",
        "Microsoft.EntityFrameworkCore": "Warning"
      }
    },
    "WriteTo": [{ "Name": "Console" }],
    "Enrich": ["FromLogContext", "WithMachineName", "WithThreadId"]
  },
  "Authentication": {
    "Audience": "{name}",
    "Issuer": "{name}-auth",
    "SecretKey": "your-secret-key-at-least-32-characters-long"
  }
}

Naming Conventions

Item	Convention	Example
Solution	PascalCase	`HumanPwr`
Projects	lowercase with dots	`humanpwr.domain`
Namespaces	lowercase	`humanpwr.domain.users`
Classes	PascalCase	`UserRepository`
Interfaces	IPascalCase	`IUserRepository`
Commands	{Action}{Entity}Command	`CreateUserCommand`
Queries	Get{Entity}Query	`GetUserByIdQuery`
Handlers	{Command/Query}Handler	`CreateUserCommandHandler`
Responses	{Entity}Response	`UserResponse`
Domain Events	{Entity}{Action}DomainEvent	`UserCreatedDomainEvent`
Errors	{Entity}Errors	`UserErrors`

Critical Rules

Domain has ZERO dependencies on other layers or external packages (except MediatR for IDomainEvent)
Application depends only on Domain - no infrastructure concerns
Infrastructure implements interfaces defined in Domain/Application
API only references Application and Infrastructure - never Domain directly for services
Use Result pattern instead of exceptions for business logic errors
Commands modify state, Queries read state (CQRS)
One handler per Command/Query - no shared handlers
Repositories are per aggregate root - not per entity
Domain events are raised in domain, handled in application layer
Always use CancellationToken in async operations

Related Skills

cqrs-command-generator - Generate Commands with handlers
cqrs-query-generator - Generate Queries with handlers
domain-entity-generator - Generate Domain entities
repository-pattern - Generate Repositories
ef-core-configuration - Generate EF configurations
result-pattern - Implement Result pattern
pipeline-behaviors - Create MediatR behaviors

dotnet-clean-architecture

.NET Clean Architecture Project Scaffolder

Overview

Architecture Layers