using System;
using System.Threading;
using System.Threading.Tasks;
using MediatR;

public class CreateOrderCommandHandler : IRequestHandler<CreateOrderCommand, Guid>
{
    private readonly IApplicationDbContext _dbContext;
    private readonly IMapper _mapper;

    public CreateOrderCommandHandler(IApplicationDbContext dbContext, IMapper mapper)
    {
        _dbContext = dbContext;
        _mapper = mapper;
    }

    public async Task<Guid> Handle(CreateOrderCommand request, CancellationToken cancellationToken)
    {
        var order = new Order
        {
            CustomerId = request.CustomerId,
            OrderDate = DateTime.UtcNow,
            Status = OrderStatus.Pending
        };

        _dbContext.Orders.Add(order);
        await _dbContext.SaveChangesAsync(cancellationToken);

        return order.Id;
    }
}

using FluentValidation;

public class CreateOrderCommandValidator : AbstractValidator<CreateOrderCommand>
{
    public CreateOrderCommandValidator()
    {
        RuleFor(x => x.CustomerId)
            .NotEmpty()
            .WithMessage("Customer ID is required");

        RuleFor(x => x.Items)
            .NotEmpty()
            .WithMessage("Order must contain at least one item");
    }
}