domain-add-aggregate

Domain Add Aggregate

Overview

This skill guides you through creating a complete Domain Aggregate with full CRUD operations following Clean Architecture, Domain-Driven Design (DDD), and bITdevKit patterns. It scaffolds code across all five layers: Domain, Infrastructure, Application, Mapping, and Presentation.

What You'll Create:

• Domain Aggregate with factory methods and change methods
• Value Objects and Enumerations (if needed)
• Domain Events (Created/Updated/Deleted)
• EF Core configuration and migration
• CQRS Commands and Queries with handlers
• Mapster DTO mappings
• Minimal API endpoints

Time Estimate: 30-60 minutes for complete aggregate with CRUD operations.

Prerequisites

Knowledge Requirements

• Domain-Driven Design (DDD): Understand aggregates, value objects, domain events
• Clean Architecture: Understand layer boundaries (Domain → Application → Infrastructure → Presentation)
• bITdevKit: Familiarity with base classes (AuditableAggregateRoot, RequestHandlerBase, etc.)
• Result Pattern: Understand Result<T> for error handling
• CQRS: Understand Commands vs Queries

Technical Requirements

• .NET 10 SDK installed (or .NET 8+ compatible)
• Project uses bITdevKit framework
• Module structure: src/Modules/[Module]/[Module].[Layer]/
• EF Core for data persistence
• Mapster for object mapping

Project Structure

This skill assumes:

src/Modules/[Module]/
├── [Module].Domain/
│   ├── Model/
│   │   └── [Entity]Aggregate/
│   └── Events/
├── [Module].Application/
│   ├── Commands/
│   └── Queries/
├── [Module].Infrastructure/
│   └── EntityFramework/
│       └── Configurations/
├── [Module].Presentation/
│   ├── Web/
│   │   └── Endpoints/
│   └── [Module]MapperRegister.cs

Core Rules

1. ALWAYS plan before coding: Create a checklist of properties, value objects, and operations
2. ALWAYS work layer-by-layer: Domain → Infrastructure → Application → Mapping → Presentation
3. NEVER reference outer layers from inner layers: Domain cannot reference Application/Infrastructure/Presentation
4. ALWAYS use factory methods returning Result<T>: No public constructors on aggregates
5. ALWAYS use private setters: Properties are immutable from outside the aggregate
6. ALWAYS register domain events: In factory methods and change methods
7. ALWAYS compile after each layer: Incremental validation prevents cascading errors
8. ALWAYS use Mapster for mapping: No manual DTO mapping in handlers
9. ALWAYS use typed entity IDs: Apply [TypedEntityId<Guid>] attribute
10. NEVER skip EF configuration: Fluent API configuration is required for all aggregates

When to Use This Skill

Use this skill when:

• Adding a new business entity (Product, Order, Invoice, etc.)
• Entity has business rules and behavior (not just data)
• Entity is the root of an aggregate (controls its lifecycle)
• You need full CRUD operations across all layers

DO NOT use this skill when:

• Adding a simple DTO (no business logic)
• Creating a read-only projection
• Entity is not an aggregate root (create as child entity instead)
• Refactoring existing aggregates (use refactoring workflows instead)

Workflows

Phase 1: Planning

Step 1: Gather Requirements

Answer these questions:

Entity Name: What is the aggregate called? (e.g., Product, Order, Invoice) Properties: What data does it hold? (Name, Description, Price, Status, etc.) Value Objects: Any complex types? (Email, Address, Money, etc.) Enumerations: Any status/type fields? (OrderStatus, ProductCategory, etc.) Business Rules: What validations? (Price > 0, Email format, Name required, etc.) Lifecycle Operations: What changes occur? (Create, Update status, Change price, etc.)

Example:

Entity: Product
Properties: Name (string), Description (string), Price (decimal), SKU (string), Status (enum)
Value Objects: Money (for Price)
Enumerations: ProductStatus (Draft, Active, Retired)
Business Rules: Name required, Price > 0, SKU unique
Operations: Create, ChangeName, ChangeDescription, ChangePrice, ChangeStatus

Step 2: Create Todo Checklist

Based on requirements, create checklist:

[ ] Domain Layer
    [ ] Create Product aggregate
    [ ] Create Money value object (if needed)
    [ ] Create ProductStatus enumeration
    [ ] Create ProductCreatedDomainEvent
    [ ] Create ProductUpdatedDomainEvent
    [ ] Create ProductDeletedDomainEvent
[ ] Infrastructure Layer
    [ ] Create ProductTypeConfiguration (EF Core)
    [ ] Add DbSet<Product> to ModuleDbContext
    [ ] Generate and apply migration
[ ] Application Layer
    [ ] Create ProductCreateCommand + Handler
    [ ] Create ProductUpdateCommand + Handler
    [ ] Create ProductDeleteCommand + Handler
    [ ] Create ProductFindOneQuery + Handler
    [ ] Create ProductFindAllQuery + Handler
[ ] Mapping Layer
    [ ] Create ProductModel DTO
    [ ] Configure Product → ProductModel mapping
    [ ] Configure value object mappings
[ ] Presentation Layer
    [ ] Create ProductEndpoints (POST, GET, PUT, DELETE)
    [ ] Register endpoints in module
[ ] Validation
    [ ] Run build and fix errors
    [ ] Test endpoints via Swagger

Phase 2: Domain Layer

Step 3: Create Aggregate Root Class

File: src/Modules/[Module]/[Module].Domain/Model/[Entity]Aggregate/[Entity].cs

Use template: [templates/aggregate-template.cs]

Key Patterns:

• Inherit from AuditableAggregateRoot<[Entity]Id>
• Apply [TypedEntityId<Guid>] attribute
• Private parameterless constructor (for EF Core)
• Private parameterized constructor (for factory)
• Public properties with private setters
• Factory method Create() returning Result<[Entity]>
• Change methods using this.Change() builder

Example:

[TypedEntityId<Guid>]
public class Product : AuditableAggregateRoot<ProductId>, IConcurrency
{
    private Product() { }

    private Product(string name, string description, decimal price, string sku)
    {
        this.Name = name;
        this.Description = description;
        this.Price = price;
        this.SKU = sku;
    }

    public string Name { get; private set; }
    public string Description { get; private set; }
    public decimal Price { get; private set; }
    public string SKU { get; private set; }
    public ProductStatus Status { get; private set; } = ProductStatus.Draft;
    public Guid ConcurrencyVersion { get; set; }

    public static Result<Product> Create(string name, string description, decimal price, string sku)
    {
        return Result<Product>.Success()
            .Ensure(_ => !string.IsNullOrWhiteSpace(name), new ValidationError("Name is required"))
            .Ensure(_ => price > 0, new ValidationError("Price must be greater than zero"))
            .Ensure(_ => !string.IsNullOrWhiteSpace(sku), new ValidationError("SKU is required"))
            .Bind(_ => new Product(name, description, price, sku))
            .Tap(e => e.DomainEvents
                .Register(new ProductCreatedDomainEvent(e))
                .Register(new EntityCreatedDomainEvent<Product>(e)));
    }

    public Result<Product> ChangeName(string name)
    {
        return this.Change()
            .Ensure(_ => !string.IsNullOrWhiteSpace(name), "Name is required")
            .Set(e => e.Name, name)
            .Register(e => new ProductUpdatedDomainEvent(e))
            .Apply();
    }

    public Result<Product> ChangePrice(decimal price)
    {
        return this.Change()
            .Ensure(_ => price > 0, "Price must be greater than zero")
            .Set(e => e.Price, price)
            .Register(e => new ProductUpdatedDomainEvent(e))
            .Apply();
    }

    public Result<Product> ChangeStatus(ProductStatus status)
    {
        return this.Change()
            .When(_ => status != null)
            .Set(e => e.Status, status)
            .Register(e => new ProductUpdatedDomainEvent(e))
            .Apply();
    }
}

Step 4: Create Value Objects (if needed)

File: src/Modules/[Module]/[Module].Domain/Model/[ValueObject].cs

Use template: [templates/value-object-template.cs]

Example (EmailAddress-like pattern):

public class Money : ValueObject
{
    private Money() { }

    private Money(decimal amount, string currency)
    {
        this.Amount = amount;
        this.Currency = currency;
    }

    public decimal Amount { get; private set; }
    public string Currency { get; private set; }

    public static Result<Money> Create(decimal amount, string currency)
    {
        return Result<Money>.Success()
            .Ensure(_ => amount >= 0, new ValidationError("Amount cannot be negative"))
            .Ensure(_ => !string.IsNullOrWhiteSpace(currency), new ValidationError("Currency is required"))
            .Bind(_ => new Money(amount, currency));
    }

    protected override IEnumerable<object> GetAtomicValues()
    {
        yield return this.Amount;
        yield return this.Currency;
    }
}

When to skip: If no complex types needed, skip this step.

Step 5: Create Enumeration (if needed)

File: src/Modules/[Module]/[Module].Domain/Model/[Entity]Aggregate/[Entity]Status.cs

Use template: [templates/enumeration-template.cs]

Example:

public partial class ProductStatus : Enumeration
{
    public static readonly ProductStatus Draft = new(1, nameof(Draft), true, "Product is in draft");
    public static readonly ProductStatus Active = new(2, nameof(Active), true, "Product is active");
    public static readonly ProductStatus Retired = new(3, nameof(Retired), true, "Product is retired");

    public bool Enabled { get; }
    public string Description { get; }
}

When to skip: If no status/type field needed, skip this step.

Step 6: Create Domain Events

Files:

• src/Modules/[Module]/[Module].Domain/Events/[Entity]CreatedDomainEvent.cs
• src/Modules/[Module]/[Module].Domain/Events/[Entity]UpdatedDomainEvent.cs
• src/Modules/[Module]/[Module].Domain/Events/[Entity]DeletedDomainEvent.cs

Use template: [templates/domain-events-template.cs]

Example:

public partial class ProductCreatedDomainEvent(Product model) : DomainEventBase
{
    public Product Model { get; private set; } = model;
}

public partial class ProductUpdatedDomainEvent(Product model) : DomainEventBase
{
    public Product Model { get; private set; } = model;
}

public partial class ProductDeletedDomainEvent(ProductId id) : DomainEventBase
{
    public ProductId Id { get; private set; } = id;
}

Step 7: Compile & Verify Domain Layer

dotnet build src/Modules/[Module]/[Module].Domain/

Expected: Build succeeds with no errors.

If errors occur:

• Check namespace declarations
• Verify bITdevKit using statements
• Confirm all required base classes are imported

Validate using checklist: [checklists/01-domain-layer.md]

Phase 3: Infrastructure Layer

Step 8: Create EF Core Type Configuration

File: src/Modules/[Module]/[Module].Infrastructure/EntityFramework/Configurations/[Entity]TypeConfiguration.cs

Use template: [templates/ef-configuration-template.cs]

Key Patterns:

• Implement IEntityTypeConfiguration<[Entity]>
• Configure table name: builder.ToTable("[Entities]")
• Configure primary key: builder.HasKey(e => e.Id)
• Configure typed ID conversion: builder.Property(e => e.Id).ValueGeneratedOnAdd().HasConversion(...)
• Configure value objects: builder.OwnsOne(e => e.Money, ...) or builder.Property(e => e.Email).HasConversion(...)
• Configure enumerations: builder.Property(e => e.Status).HasConversion(...)
• Ignore domain events: builder.Ignore(e => e.DomainEvents)
• Configure concurrency: builder.Property(e => e.ConcurrencyVersion).IsConcurrencyToken()

Example:

public class ProductTypeConfiguration : IEntityTypeConfiguration<Product>
{
    public void Configure(EntityTypeBuilder<Product> builder)
    {
        builder.ToTable("Products");

        builder.HasKey(e => e.Id);

        builder.Property(e => e.Id)
            .ValueGeneratedOnAdd()
            .HasConversion(
                id => id.Value,
                value => ProductId.Create(value));

        builder.Property(e => e.Name).IsRequired().HasMaxLength(256);
        builder.Property(e => e.Description).HasMaxLength(1024);
        builder.Property(e => e.Price).HasColumnType("decimal(18,2)");
        builder.Property(e => e.SKU).IsRequired().HasMaxLength(50);

        builder.Property(e => e.Status)
            .HasConversion(
                s => s.Id,
                id => Enumeration.FromId<ProductStatus>(id));

        builder.Property(e => e.ConcurrencyVersion).IsConcurrencyToken();

        builder.Ignore(e => e.DomainEvents);
    }
}

Step 9: Add DbSet to Module DbContext

File: src/Modules/[Module]/[Module].Infrastructure/EntityFramework/[Module]DbContext.cs

Add DbSet property:

public DbSet<Product> Products => this.Set<Product>();

Step 10: Generate EF Core Migration

# From solution root
dotnet ef migrations add Add[Entity] --project src/Modules/[Module]/[Module].Infrastructure --startup-project src/Presentation.Web.Server --context [Module]DbContext

Example:

dotnet ef migrations add AddProduct --project src/Modules/CoreModule/CoreModule.Infrastructure --startup-project src/Presentation.Web.Server --context CoreModuleDbContext

Review migration file: Verify it creates correct table and columns.

Step 11: Compile & Verify Infrastructure Layer

dotnet build src/Modules/[Module]/[Module].Infrastructure/

Expected: Build succeeds with no errors.

Validate using checklist: [checklists/02-infrastructure-layer.md]

Phase 4: Application Layer

Step 12: Create Command (Create Operation)

File: src/Modules/[Module]/[Module].Application/Commands/[Entity]CreateCommand.cs

Use template: [templates/command-create-template.cs]

Example:

public class ProductCreateCommand : IRequest<Result<ProductModel>>
{
    public string Name { get; init; }
    public string Description { get; init; }
    public decimal Price { get; init; }
    public string SKU { get; init; }
}

public class ProductCreateCommandValidator : AbstractValidator<ProductCreateCommand>
{
    public ProductCreateCommandValidator()
    {
        this.RuleFor(c => c.Name).NotEmpty().MaximumLength(256);
        this.RuleFor(c => c.Price).GreaterThan(0);
        this.RuleFor(c => c.SKU).NotEmpty().MaximumLength(50);
    }
}

Step 13: Create Command Handler (Create Operation)

File: src/Modules/[Module]/[Module].Application/Commands/[Entity]CreateCommandHandler.cs

Use template: [templates/command-create-handler-template.cs]

Key Patterns:

• Inherit from RequestHandlerBase<TRequest, TResponse>
• Inject IGenericRepository<[Entity]> and IMapper
• Apply [Retry] and [Timeout] attributes
• Use Result<T> pattern throughout
• Call aggregate factory method: [Entity].Create(...)
• Insert via repository: await repository.InsertAsync(...)
• Map to DTO: mapper.Map<[Entity], [Entity]Model>(...)

Example:

[Retry(2)]
[Timeout(30)]
public class ProductCreateCommandHandler(IGenericRepository<Product> repository, IMapper mapper)
    : RequestHandlerBase<ProductCreateCommand, Result<ProductModel>>
{
    public override async Task<Result<ProductModel>> Process(
        ProductCreateCommand request,
        CancellationToken cancellationToken)
    {
        var productResult = Product.Create(
            request.Name,
            request.Description,
            request.Price,
            request.SKU);

        if (productResult.IsFailure)
        {
            return Result<ProductModel>.Failure().WithMessages(productResult.Messages);
        }

        var product = await repository.InsertAsync(productResult.Value, cancellationToken);

        return mapper.Map<Product, ProductModel>(product);
    }
}

Step 14: Create Command (Update Operation)

File: src/Modules/[Module]/[Module].Application/Commands/[Entity]UpdateCommand.cs

Use template: [templates/command-update-template.cs]

Example:

public class ProductUpdateCommand : IRequest<Result<ProductModel>>
{
    public Guid Id { get; init; }
    public string Name { get; init; }
    public string Description { get; init; }
    public decimal Price { get; init; }
}

public class ProductUpdateCommandValidator : AbstractValidator<ProductUpdateCommand>
{
    public ProductUpdateCommandValidator()
    {
        this.RuleFor(c => c.Id).NotEmpty();
        this.RuleFor(c => c.Name).NotEmpty().MaximumLength(256);
        this.RuleFor(c => c.Price).GreaterThan(0);
    }
}

Step 15: Create Command Handler (Update Operation)

File: src/Modules/[Module]/[Module].Application/Commands/[Entity]UpdateCommandHandler.cs

Use template: [templates/command-update-handler-template.cs]

Key Patterns:

• Find entity: await repository.FindOneAsync(id, ...)
• Check if exists: Return Result.Failure() if not found
• Call change methods: entity.ChangeName(...).ChangePrice(...)
• Update via repository: await repository.UpdateAsync(...)

Example:

[Retry(2)]
[Timeout(30)]
public class ProductUpdateCommandHandler(IGenericRepository<Product> repository, IMapper mapper)
    : RequestHandlerBase<ProductUpdateCommand, Result<ProductModel>>
{
    public override async Task<Result<ProductModel>> Process(
        ProductUpdateCommand request,
        CancellationToken cancellationToken)
    {
        var product = await repository.FindOneAsync(
            ProductId.Create(request.Id),
            cancellationToken: cancellationToken);

        if (product == null)
        {
            return Result<ProductModel>.Failure($"Product with ID {request.Id} not found");
        }

        var nameResult = product.ChangeName(request.Name);
        if (nameResult.IsFailure)
        {
            return Result<ProductModel>.Failure().WithMessages(nameResult.Messages);
        }

        var priceResult = product.ChangePrice(request.Price);
        if (priceResult.IsFailure)
        {
            return Result<ProductModel>.Failure().WithMessages(priceResult.Messages);
        }

        await repository.UpdateAsync(product, cancellationToken);

        return mapper.Map<Product, ProductModel>(product);
    }
}

Step 16: Create Command (Delete Operation)

File: src/Modules/[Module]/[Module].Application/Commands/[Entity]DeleteCommand.cs

Use template: [templates/command-delete-template.cs]

Example:

public class ProductDeleteCommand : IRequest<Result>
{
    public Guid Id { get; init; }
}

public class ProductDeleteCommandValidator : AbstractValidator<ProductDeleteCommand>
{
    public ProductDeleteCommandValidator()
    {
        this.RuleFor(c => c.Id).NotEmpty();
    }
}

Step 17: Create Command Handler (Delete Operation)

File: src/Modules/[Module]/[Module].Application/Commands/[Entity]DeleteCommandHandler.cs

Use template: [templates/command-delete-handler-template.cs]

Example:

[Retry(2)]
[Timeout(30)]
public class ProductDeleteCommandHandler(IGenericRepository<Product> repository)
    : RequestHandlerBase<ProductDeleteCommand, Result>
{
    public override async Task<Result> Process(
        ProductDeleteCommand request,
        CancellationToken cancellationToken)
    {
        var product = await repository.FindOneAsync(
            ProductId.Create(request.Id),
            cancellationToken: cancellationToken);

        if (product == null)
        {
            return Result.Failure($"Product with ID {request.Id} not found");
        }

        product.DomainEvents.Register(new ProductDeletedDomainEvent(product.Id));

        await repository.DeleteAsync(product, cancellationToken);

        return Result.Success();
    }
}

Step 18: Create Query (FindOne Operation)

File: src/Modules/[Module]/[Module].Application/Queries/[Entity]FindOneQuery.cs

Use template: [templates/query-findone-template.cs]

Example:

public class ProductFindOneQuery : IRequest<Result<ProductModel>>
{
    public Guid Id { get; init; }
}

public class ProductFindOneQueryValidator : AbstractValidator<ProductFindOneQuery>
{
    public ProductFindOneQueryValidator()
    {
        this.RuleFor(q => q.Id).NotEmpty();
    }
}

Step 19: Create Query Handler (FindOne Operation)

File: src/Modules/[Module]/[Module].Application/Queries/[Entity]FindOneQueryHandler.cs

Use template: [templates/query-findone-handler-template.cs]

Example:

[Timeout(30)]
public class ProductFindOneQueryHandler(IGenericRepository<Product> repository, IMapper mapper)
    : RequestHandlerBase<ProductFindOneQuery, Result<ProductModel>>
{
    public override async Task<Result<ProductModel>> Process(
        ProductFindOneQuery request,
        CancellationToken cancellationToken)
    {
        var product = await repository.FindOneAsync(
            ProductId.Create(request.Id),
            cancellationToken: cancellationToken);

        if (product == null)
        {
            return Result<ProductModel>.Failure($"Product with ID {request.Id} not found");
        }

        return mapper.Map<Product, ProductModel>(product);
    }
}

Step 20: Create Query (FindAll Operation)

File: src/Modules/[Module]/[Module].Application/Queries/[Entity]FindAllQuery.cs

Use template: [templates/query-findall-template.cs]

Example:

public class ProductFindAllQuery : IRequest<Result<IEnumerable<ProductModel>>>
{
    // Optional: Add filtering/sorting parameters
}

public class ProductFindAllQueryValidator : AbstractValidator<ProductFindAllQuery>
{
    public ProductFindAllQueryValidator()
    {
        // No validation needed for basic find all
    }
}

Step 21: Create Query Handler (FindAll Operation)

File: src/Modules/[Module]/[Module].Application/Queries/[Entity]FindAllQueryHandler.cs

Use template: [templates/query-findall-handler-template.cs]

Example:

[Timeout(30)]
public class ProductFindAllQueryHandler(IGenericRepository<Product> repository, IMapper mapper)
    : RequestHandlerBase<ProductFindAllQuery, Result<IEnumerable<ProductModel>>>
{
    public override async Task<Result<IEnumerable<ProductModel>>> Process(
        ProductFindAllQuery request,
        CancellationToken cancellationToken)
    {
        var products = await repository.FindAllAsync(cancellationToken: cancellationToken);

        return Result<IEnumerable<ProductModel>>.Success(
            products.Select(p => mapper.Map<Product, ProductModel>(p)));
    }
}

Step 22: Compile & Verify Application Layer

dotnet build src/Modules/[Module]/[Module].Application/

Expected: Build succeeds with no errors.

Validate using checklist: [checklists/03-application-layer.md]

Phase 5: Mapping Layer

Step 23: Create DTO Model

File: src/Modules/[Module]/[Module].Presentation/[Entity]Model.cs

Use template: [templates/model-template.cs]

Example:

public class ProductModel
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public decimal Price { get; set; }
    public string SKU { get; set; }
    public string Status { get; set; }
    public DateTime CreatedDate { get; set; }
    public DateTime? UpdatedDate { get; set; }
}

Step 24: Update Mapper Register

File: src/Modules/[Module]/[Module].Presentation/[Module]MapperRegister.cs

Use template: [templates/mapper-register-template.cs]

Add mapping configurations:

public class CoreModuleMapperRegister : IRegister
{
    public void Register(TypeAdapterConfig config)
    {
        // Existing mappings...

        // Product mappings
        config.ForType<Product, ProductModel>()
            .Map(dest => dest.Id, src => src.Id.Value)
            .Map(dest => dest.Status, src => src.Status.Name);

        // Value object conversions (if applicable)
        config.NewConfig<Money, decimal>()
            .MapWith(src => src.Amount);
    }
}

Step 25: Compile & Verify Mapping Layer

dotnet build src/Modules/[Module]/[Module].Presentation/

Expected: Build succeeds with no errors.

Validate using checklist: [checklists/04-mapping-layer.md]

Phase 6: Presentation Layer

Step 26: Create API Endpoints

File: src/Modules/[Module]/[Module].Presentation/Web/Endpoints/[Entity]Endpoints.cs

Use template: [templates/endpoint-template.cs]

Example:

public static class ProductEndpoints
{
    public static IEndpointRouteBuilder MapProductEndpoints(this IEndpointRouteBuilder app)
    {
        app.MapPost("api/core/products", CreateProduct)
            .WithName("CreateProduct")
            .WithTags("Products")
            .Produces<ProductModel>(StatusCodes.Status201Created)
            .Produces<ProblemDetails>(StatusCodes.Status400BadRequest);

        app.MapGet("api/core/products/{id:guid}", GetProduct)
            .WithName("GetProduct")
            .WithTags("Products")
            .Produces<ProductModel>(StatusCodes.Status200OK)
            .Produces<ProblemDetails>(StatusCodes.Status404NotFound);

        app.MapGet("api/core/products", GetAllProducts)
            .WithName("GetAllProducts")
            .WithTags("Products")
            .Produces<IEnumerable<ProductModel>>(StatusCodes.Status200OK);

        app.MapPut("api/core/products/{id:guid}", UpdateProduct)
            .WithName("UpdateProduct")
            .WithTags("Products")
            .Produces<ProductModel>(StatusCodes.Status200OK)
            .Produces<ProblemDetails>(StatusCodes.Status404NotFound);

        app.MapDelete("api/core/products/{id:guid}", DeleteProduct)
            .WithName("DeleteProduct")
            .WithTags("Products")
            .Produces(StatusCodes.Status204NoContent)
            .Produces<ProblemDetails>(StatusCodes.Status404NotFound);

        return app;
    }

    private static async Task<IResult> CreateProduct(
        [FromServices] IRequester requester,
        [FromBody] ProductCreateCommand command)
    {
        var result = await requester.RequestAsync(command);
        return result.IsSuccess
            ? Results.Created($"/api/core/products/{result.Value.Id}", result.Value)
            : Results.BadRequest(result.ToProblemDetails());
    }

    private static async Task<IResult> GetProduct(
        [FromServices] IRequester requester,
        Guid id)
    {
        var result = await requester.RequestAsync(new ProductFindOneQuery { Id = id });
        return result.IsSuccess
            ? Results.Ok(result.Value)
            : Results.NotFound(result.ToProblemDetails());
    }

    private static async Task<IResult> GetAllProducts(
        [FromServices] IRequester requester)
    {
        var result = await requester.RequestAsync(new ProductFindAllQuery());
        return result.IsSuccess
            ? Results.Ok(result.Value)
            : Results.BadRequest(result.ToProblemDetails());
    }

    private static async Task<IResult> UpdateProduct(
        [FromServices] IRequester requester,
        Guid id,
        [FromBody] ProductUpdateCommand command)
    {
        var commandWithId = command with { Id = id };
        var result = await requester.RequestAsync(commandWithId);
        return result.IsSuccess
            ? Results.Ok(result.Value)
            : Results.NotFound(result.ToProblemDetails());
    }

    private static async Task<IResult> DeleteProduct(
        [FromServices] IRequester requester,
        Guid id)
    {
        var result = await requester.RequestAsync(new ProductDeleteCommand { Id = id });
        return result.IsSuccess
            ? Results.NoContent()
            : Results.NotFound(result.ToProblemDetails());
    }
}

Step 27: Register Endpoints in Module

File: src/Modules/[Module]/[Module].Presentation/[Module]Module.cs

Add endpoint registration:

app.MapProductEndpoints();

Step 28: Compile & Verify Presentation Layer

dotnet build src/Modules/[Module]/[Module].Presentation/

Expected: Build succeeds with no errors.

Validate using checklist: [checklists/05-presentation-layer.md]

Phase 7: Final Validation

Step 29: Build Entire Solution

dotnet build

Expected: Build succeeds with no errors.

If errors occur:

• Review error messages carefully
• Common issues: missing using statements, typos in class/property names, incorrect namespaces
• Use dotnet build --verbosity detailed for more information

Step 30: Apply Migrations (if not already applied)

dotnet ef database update --project src/Modules/[Module]/[Module].Infrastructure --startup-project src/Presentation.Web.Server --context [Module]DbContext

Expected: Database updated with new table.

Step 31: Run Application and Test with Swagger

dotnet run --project src/Presentation.Web.Server

Navigate to: https://localhost:5001/swagger

Test Endpoints:

1. POST /api/core/products: Create new product
2. GET /api/core/products: List all products
3. GET /api/core/products/{id}: Get single product
4. PUT /api/core/products/{id}: Update product
5. DELETE /api/core/products/{id}: Delete product

Validate using checklist: [checklists/quality-gates.md]

Step 32: Mark Complete

Congratulations! You've successfully created a complete Domain Aggregate with full CRUD operations across all five layers.

Created Files Summary (for Product example):

Domain Layer (7 files):
- Product.cs (aggregate)
- Money.cs (value object, if created)
- ProductStatus.cs (enumeration)
- ProductCreatedDomainEvent.cs
- ProductUpdatedDomainEvent.cs
- ProductDeletedDomainEvent.cs

Infrastructure Layer (2 files):
- ProductTypeConfiguration.cs
- Add[Entity] migration

Application Layer (10 files):
- ProductCreateCommand.cs + ProductCreateCommandHandler.cs
- ProductUpdateCommand.cs + ProductUpdateCommandHandler.cs
- ProductDeleteCommand.cs + ProductDeleteCommandHandler.cs
- ProductFindOneQuery.cs + ProductFindOneQueryHandler.cs
- ProductFindAllQuery.cs + ProductFindAllQueryHandler.cs

Presentation Layer (2 files):
- ProductModel.cs (DTO)
- ProductEndpoints.cs

Total: ~21 files

Examples

Example 1: Simple Aggregate (Product)

User: "Add a Product aggregate with Name, Description, Price, and SKU properties"

Actions:

1. Planning: Identify no value objects needed, ProductStatus enumeration needed
2. Domain: Create Product.cs, ProductStatus.cs, 3 domain events
3. Infrastructure: Create ProductTypeConfiguration.cs, generate migration
4. Application: Create 5 command/query pairs with handlers
5. Mapping: Create ProductModel.cs, update MapperRegister
6. Presentation: Create ProductEndpoints.cs
7. Validation: Build, test with Swagger

Result: Complete Product aggregate with CRUD operations (~20 files)

Example 2: Aggregate with Value Object (Customer)

User: "Add a Customer aggregate with FirstName, LastName, Email (value object), and Status"

Actions:

1. Planning: EmailAddress value object needed, CustomerStatus enumeration needed
2. Domain: Create Customer.cs, EmailAddress.cs, CustomerStatus.cs, 3 domain events
3. Infrastructure: Create CustomerTypeConfiguration.cs (with value object conversion), generate migration
4. Application: Create 5 command/query pairs with handlers
5. Mapping: Create CustomerModel.cs, update MapperRegister (with EmailAddress → string conversion)
6. Presentation: Create CustomerEndpoints.cs
7. Validation: Build, test with Swagger

Result: Complete Customer aggregate with value object (~22 files)

Quality Checklist

Before considering aggregate complete:

• Domain Layer: Aggregate compiles, factory method returns Result<T>, change methods use Change() builder
• Infrastructure Layer: EF configuration complete, migration generated and applied
• Application Layer: Commands/Queries/Handlers compile, validators present, retry/timeout attributes applied
• Mapping Layer: DTO model created, Mapster configurations registered
• Presentation Layer: Endpoints created (POST, GET, PUT, DELETE), registered in module
• Build: Solution builds without errors
• Database: Migration applied successfully
• Swagger: All endpoints visible and testable
• Functional Test: Can create, read, update, delete via Swagger

Common Pitfalls

WRONG:

• Public constructors on aggregates (use factory methods)
• Public setters on properties (use private setters)
• Forgetting to register domain events
• Skipping EF configuration (fluent API required)
• Manual mapping in handlers (use IMapper)
• Missing validators on commands/queries
• Forgetting to compile after each layer

CORRECT:

• Private constructors + factory methods returning Result<T>
• Private setters on all properties
• Domain events registered in factory and change methods
• Complete EF configuration with typed ID conversion
• Mapster for all domain ↔ DTO mapping
• FluentValidation validators on all commands/queries
• Incremental compilation and validation

File Naming Conventions

• Aggregate: [Entity].cs (e.g., Product.cs)
• Value Object: [Name].cs (e.g., EmailAddress.cs)
• Enumeration: [Entity][Type].cs (e.g., ProductStatus.cs)
• Domain Event: [Entity][Action]DomainEvent.cs (e.g., ProductCreatedDomainEvent.cs)
• EF Configuration: [Entity]TypeConfiguration.cs (e.g., ProductTypeConfiguration.cs)
• Command: [Entity][Action]Command.cs (e.g., ProductCreateCommand.cs)
• Command Handler: [Entity][Action]CommandHandler.cs (e.g., ProductCreateCommandHandler.cs)
• Query: [Entity][Action]Query.cs (e.g., ProductFindOneQuery.cs)
• Query Handler: [Entity][Action]QueryHandler.cs (e.g., ProductFindOneQueryHandler.cs)
• DTO Model: [Entity]Model.cs (e.g., ProductModel.cs)
• Endpoints: [Entity]Endpoints.cs (e.g., ProductEndpoints.cs)

References

Project Documentation

• Project Architecture: AGENTS.md
• Module Structure: src/Modules/CoreModule/CoreModule-README.md
• ADRs: docs/ADR/ (especially ADR-0001, ADR-0003, ADR-0005, ADR-0012)

bITdevKit Documentation

• bITdevKit GitHub: https://github.com/BridgingIT-GmbH/bITdevKit
• bITdevKit Docs: https://github.com/BridgingIT-GmbH/bITdevKit/tree/main/docs

External References

• Clean Architecture: https://blog.cleancoder.com/uncle-bob/2012/08/13/the-clean-architecture.html
• Domain-Driven Design: https://martinfowler.com/bliki/DomainDrivenDesign.html
• Result Pattern: https://enterprisecraftsmanship.com/posts/error-handling-exception-or-result/
• CQRS: https://martinfowler.com/bliki/CQRS.html

Templates

• See: .github/skills/domain-add-aggregate/templates/ for all code templates

Examples

• See: .github/skills/domain-add-aggregate/examples/ for complete walkthroughs

Checklists

• See: .github/skills/domain-add-aggregate/checklists/ for layer-specific validation