CQRS Command Generator

Command Record

namespace {Company}.{Domain}.Application.Features.Orders.Commands.Create;

public sealed record CreateOrderCommand(
    string CustomerName,
    decimal Total,
    List<CreateOrderItemDto> Items) : IRequest<Result<Guid>>;

public sealed record CreateOrderItemDto(
    string ProductName,
    int Quantity,
    decimal UnitPrice);

Validator

namespace {Company}.{Domain}.Application.Features.Orders.Commands.Create;

internal sealed class CreateOrderCommandValidator
    : AbstractValidator<CreateOrderCommand>
{
    public CreateOrderCommandValidator()
    {
        RuleFor(x => x.CustomerName)
            .NotEmpty().WithMessage("Customer name is required")
            .MaximumLength(200);

        RuleFor(x => x.Total)
            .GreaterThan(0).WithMessage("Total must be positive");

        RuleFor(x => x.Items)
            .NotEmpty().WithMessage("At least one item is required");

        RuleForEach(x => x.Items).ChildRules(item =>
        {
            item.RuleFor(i => i.ProductName).NotEmpty();
            item.RuleFor(i => i.Quantity).GreaterThan(0);
            item.RuleFor(i => i.UnitPrice).GreaterThan(0);
        });
    }
}

Handler

namespace {Company}.{Domain}.Application.Features.Orders.Commands.Create;

internal sealed class CreateOrderCommandHandler(
    IUnitOfWork unitOfWork)
    : IRequestHandler<CreateOrderCommand, Result<Guid>>
{
    public async Task<Result<Guid>> Handle(
        CreateOrderCommand request, CancellationToken cancellationToken)
    {
        var order = Order.Create(
            request.CustomerName,
            request.Total,
            request.Items.Select(i => new OrderItem(
                i.ProductName, i.Quantity, i.UnitPrice)).ToList());

        await unitOfWork.Orders.AddAsync(order, cancellationToken);
        await unitOfWork.SaveChangesAsync(cancellationToken);

        return Result<Guid>.Success(order.Id);
    }
}

Update Command Pattern

public sealed record UpdateOrderCommand(
    Guid Id,
    string CustomerName,
    decimal Total) : IRequest<Result>;

internal sealed class UpdateOrderCommandHandler(
    IUnitOfWork unitOfWork)
    : IRequestHandler<UpdateOrderCommand, Result>
{
    public async Task<Result> Handle(
        UpdateOrderCommand request, CancellationToken cancellationToken)
    {
        var order = await unitOfWork.Orders.FindAsync(
            request.Id, cancellationToken);

        if (order is null)
            return Result.Failure("Order not found");

        order.Update(request.CustomerName, request.Total);
        await unitOfWork.SaveChangesAsync(cancellationToken);

        return Result.Success();
    }
}

Delete Command Pattern

public sealed record DeleteOrderCommand(Guid Id) : IRequest<Result>;

internal sealed class DeleteOrderCommandHandler(
    IUnitOfWork unitOfWork)
    : IRequestHandler<DeleteOrderCommand, Result>
{
    public async Task<Result> Handle(
        DeleteOrderCommand request, CancellationToken cancellationToken)
    {
        var order = await unitOfWork.Orders.FindAsync(
            request.Id, cancellationToken);

        if (order is null)
            return Result.Failure("Order not found");

        unitOfWork.Orders.Remove(order);
        await unitOfWork.SaveChangesAsync(cancellationToken);

        return Result.Success();
    }
}

File Structure (Feature Folder)

Application/Features/Orders/Commands/
├── Create/
│   ├── CreateOrderCommand.cs
│   ├── CreateOrderCommandValidator.cs
│   └── CreateOrderCommandHandler.cs
├── Update/
│   ├── UpdateOrderCommand.cs
│   ├── UpdateOrderCommandValidator.cs
│   └── UpdateOrderCommandHandler.cs
└── Delete/
    ├── DeleteOrderCommand.cs
    └── DeleteOrderCommandHandler.cs

Anti-Patterns

Anti-Pattern	Correct Approach
Command with mutable properties	Use sealed record (immutable)
Validation in handler	Use FluentValidation + pipeline behavior
Returning domain entity from handler	Return Result<T> with ID or DTO
Handler accessing DbContext directly	Use IUnitOfWork or IRepository

Detect Existing Patterns

grep -r "IRequest<\|IRequestHandler<" --include="*.cs"
grep -r "AbstractValidator<" --include="*.cs"

Adding to Existing Project

1. Add MediatR and FluentValidation NuGet packages
2. Register with AddMediatR and AddValidatorsFromAssembly
3. Add ValidationBehavior<,> pipeline behavior
4. Create feature folder per aggregate/entity