Ticketing 工单模块架构概览：多租户协作、SLA 履约与事件驱动

using System;
using System.ComponentModel;
using BitzOrcas.Domain.Entities;
using BitzOrcas.Domain.Results;
using BitzOrcas.Persistence.Metadata;

namespace BitzOrcas.Ticket.Domain;

public static class TicketErrors
{
    public static readonly Error AlreadyClosed =
        Error.Conflict("Ticket.AlreadyClosed", "已关闭的工单无法指派。");

    public static readonly Error NotFound =
        Error.NotFound("Ticket.NotFound", "工单不存在。");
}

[BitzTable("SysTicket", IsTenant = true, IsSoftDelete = true, Description = "业务工单主表")]
[BitzIndex("IX_SysTicket_Status_Tenant", nameof(Status), nameof(TenantId))]
public sealed class Ticket : TenantAggregateRoot<string>
{
    [BitzColumn(Length = 200, IsRequired = true)]
    public string Title { get; private set; } = string.Empty;

    [BitzColumn(Length = 4000, IsRequired = true)]
    public string Description { get; private set; } = string.Empty;

    [BitzColumn(IsRequired = true)]
    public TicketPriority Priority { get; private set; } = TicketPriority.Medium;

    [BitzColumn(IsRequired = true)]
    public TicketStatus Status { get; private set; } = TicketStatus.Open;

    [BitzColumn(Length = 64)]
    public string? AssigneeUserId { get; private set; }

    [BitzColumn(IsRequired = true)]
    public DateTimeOffset SlaResponseDueAt { get; private set; }

    [Obsolete("仅供 ORM 持久化物化使用。请使用 Create 工厂方法。", error: true)]
    [EditorBrowsable(EditorBrowsableState.Never)]
    public Ticket()
        : base("0")
    {
    }

    // 领域方法：指派工单并进入处理中
    public Result AssignTo(string engineerUserId, string operatorId, DateTimeOffset now)
    {
        if (Status == TicketStatus.Closed || Status == TicketStatus.Resolved)
        {
            return Result.Failure(TicketErrors.AlreadyClosed);
        }

        AssigneeUserId = engineerUserId;
        Status = TicketStatus.InProgress;

        // 产生指派领域事件
        AddDomainEvent(new TicketAssignedDomainEvent(Id, TenantId, engineerUserId, operatorId, now));

        return Result.Success();
    }
}

using System.Threading;
using System.Threading.Tasks;
using BitzOrcas.Application.Abstractions.Security;
using BitzOrcas.Domain.Abstractions;
using BitzOrcas.Domain.Results;
using BitzOrcas.Ticket.Domain;

public sealed class AssignTicketCommandHandler(
    ICommandRepository<Ticket, string> ticketRepo,
    ICurrentUser currentUser,
    IAppClock clock)
{
    public async ValueTask<Result> Handle(AssignTicketCommand command, CancellationToken ct)
    {
        // 1. 加载目标工单聚合
        var ticketResult = await ticketRepo.FindAsync(command.TicketId, ct);
        if (ticketResult.IsFailure)
        {
            return Result.Failure(TicketErrors.NotFound);
        }

        var ticket = ticketResult.Value;

        // 2. 执行领域指派
        var assignResult = ticket.AssignTo(command.AssigneeUserId, currentUser.UserId, clock.UtcNow);
        if (assignResult.IsFailure) return assignResult;

        // 3. 持久化聚合（自动检查乐观并发版本，由 TransactionPipeline 提交）
        await ticketRepo.UpdateAsync(ticket, ct);

        return Result.Success();
    }
}