如何在cqrs模式中使用eventstore

本文关键字:eventstore 模式 cqrs | 更新日期: 2023-09-27 18:19:06

我正在研究CQRS模式。我已经创建了一个与此方法相关的项目,我可以在其中插入和检索数据。我开始知道有两种不同的模型写模型(命令)和读模型(查询)。我只是想知道我写模型的方法是否正确。以及如何在多个用户执行相同操作时使用临时数据库进行事件溯源。

Command.cs

public class Command : Message
{
}
public class Insert : Command
{
    public readonly Guid Id;
    public readonly string Name;
    public Insert(Guid id, string name)
    {
        Id = id;
        Name = name;
    }
}
public class Update : Command
{
    public readonly Guid Id;
    public readonly string NewName;
    public readonly int OriginalVersion;
    public Update(Guid id, string newName)
    {
        Id = id;
        NewName = newName;
    }
}
public class Delete : Command
{
    public Guid Id;
    public readonly int OriginalVersion;
    public Delete(Guid id)
    {
        Id = id;
    }
}

Event.cs

public class Event:Message
{
    public int Version;
}
public class Inserted : Event
{
    public readonly Guid Id;
    public readonly string Name;
    public Inserted(Guid id, string name)
    {
        Id = id;
        Name = name;
    }
}
public class Updated : Event
{
    public readonly Guid Id;
    public readonly string NewName;
    public readonly int OriginalVersion;
    public Updated(Guid id, string newName)
    {
        Id = id;
        NewName = newName;
    }
}
public class Deleted : Event
{
    public Guid Id;
    public Deleted(Guid id)
    {
        Id = id;
    }
}

EventStore.cs

public interface IEventStore
{
    void SaveEvents(Guid aggregateId, IEnumerable<Event> events, int expectedVersion);
    List<Event> GetEventsForAggregate(Guid aggregateId);
}
public class EventStore : IEventStore
{
    private readonly IEventPublisher _publisher;
    private struct EventDescriptor
    {
        public readonly Event EventData;
        public readonly Guid Id;
        public readonly int Version;
        public EventDescriptor(Guid id, Event eventData, int version)
        {
            EventData = eventData;
            Version = version;
            Id = id;
        }
    }
    public EventStore(IEventPublisher publisher)
    {
        _publisher = publisher;
    }
    private readonly Dictionary<Guid, List<EventDescriptor>> _current = new Dictionary<Guid, List<EventDescriptor>>();
    public void SaveEvents(Guid aggregateId, IEnumerable<Event> events, int expectedVersion)
    {
        List<EventDescriptor> eventDescriptors;
        if (!_current.TryGetValue(aggregateId, out eventDescriptors))
        {
            eventDescriptors = new List<EventDescriptor>();
            _current.Add(aggregateId, eventDescriptors);
        }
        else if (eventDescriptors[eventDescriptors.Count - 1].Version != expectedVersion && expectedVersion != -1)
        {
            throw new ConcurrencyException();
        }
        var i = expectedVersion;
        foreach (var @event in events)
        {
            i++;
            @event.Version = i;
            eventDescriptors.Add(new EventDescriptor(aggregateId, @event, i));
            _publisher.Publish(@event);
        }
    }
    public List<Event> GetEventsForAggregate(Guid aggregateId)
    {
        List<EventDescriptor> eventDescriptors;
        if (!_current.TryGetValue(aggregateId, out eventDescriptors))
        {
            throw new AggregateNotFoundException();
        }
        return eventDescriptors.Select(desc => desc.EventData).ToList();
    }
}
public class AggregateNotFoundException : Exception
{
}
public class ConcurrencyException : Exception
{
}

ReadModel.cs

 public interface IReadModelFacade
 {
     IEnumerable<InventoryItemListDto> GetInventoryItems();
     InventoryItemDetailsDto GetInventoryItemDetails(Guid id);
 }
 public class InventoryItemDetailsDto
 {
     public Guid Id;
     public string Name;
     public int CurrentCount;
     public int Version;
     public InventoryItemDetailsDto(Guid id, string name, int currentCount, int version)
     {
         Id = id;
         Name = name;
         CurrentCount = currentCount;
         Version = version;
     }
 }
 public class InventoryItemListDto
 {
     public Guid Id;
     public string Name;
     public InventoryItemListDto(Guid id, string name)
     {
         Id = id;
         Name = name;
     }
 }
 public class InventoryListView : Handles<Inserted>, Handles<Updated>
 {
     public void Handle(Inserted message)
     {
         BullShitDatabase.list.Add(new InventoryItemListDto(message.Id, message.Name));
     }
     public void Handle(Updated message)
     {
         var item = BullShitDatabase.list.Find(x => x.Id == message.Id);
         item.Name = message.NewName;
     }
 }
 public class InvenotryItemDetailView : Handles<Inserted>, Handles<Updated>
 {
     public void Handle(Inserted message)
     {
         BullShitDatabase.details.Add(message.Id, new InventoryItemDetailsDto(message.Id, message.Name, 0, 0));
     }
     public void Handle(Updated message)
     {
         InventoryItemDetailsDto d = GetDetailsItem(message.Id);
         d.Name = message.NewName;
         d.Version = message.Version;
     }
     private InventoryItemDetailsDto GetDetailsItem(Guid id)
     {
         InventoryItemDetailsDto d;
         if (!BullShitDatabase.details.TryGetValue(id, out d))
         {
             throw new InvalidOperationException("did not find the original inventory this shouldnt happen");
         }
         return d;
     }
 }
 public class ReadModelFacade : IReadModelFacade
 {
     public IEnumerable<InventoryItemListDto> GetInventoryItems()
     {
         return BullShitDatabase.list;
     }
     public InventoryItemDetailsDto GetInventoryItemDetails(Guid id)
     {
         return BullShitDatabase.details[id];
     }
 }
 public static class BullShitDatabase
 {
     public static Dictionary<Guid, InventoryItemDetailsDto> details = new Dictionary<Guid, InventoryItemDetailsDto>();
     public static List<InventoryItemListDto> list = new List<InventoryItemListDto>();
  }

如何在cqrs模式中使用eventstore

不管你是使用EventStore还是任何其他存储机制,你都应该针对接口(契约)进行编码。

但是首先,您的命令IMO没有正确定义,它们应该是携带数据并表示域操作(CRUD或非CRUD)的不可变对象,那么为什么要在命令中定义方法?

将命令定义为类不是问题,您最终需要一个,但为什么不将接口作为所有命令的基本类型呢?(固体原则)

所有的类名(命令/事件)必须是有意义的,也就是说,更新,删除…不要说太多,真的。

我也没看到你的服务层在哪里。服务层应该负责处理命令,那么您打算如何做到这一点呢?

下面你有一个例子,我将如何做(有点抽象,但它给你一个想法):

// Message definitions
public interface IMessage
{
    Guid ID {get; set;}
}
public interface IEvent : IMessage
{ }
public interface ICommand : IMessage
{ }
public class DeleteUserCommand : ICommand
{
    public Guid ID {get; set;}
    public Guid UserId {get; set;}
}
public class UserDeletedEvent : IEvent
{
    public Guid ID {get; set;}
    public Guid UserId {get; set;}
}
// Repository definitions
public interface IRepository
{ }
public interface IUserRepository : IRepository
{
    void DeleteUser(Guid userId);
}
public UserRepository : IUserRepository
{
    public void DeleteUser(Guid userId)
    {}
}
// Service definitions
public interface IService
{ }
public class UserService : IService, IHandles<DeleteUserCommand>
{
    public IUserRepository UserRepository {get; set;}
    public void Handle(DeleteUserCommand deleteUserCommand)
    {
        UserRepository.DeleteUser(deleteUserCommand.Id)
        //raise event
    }
}