如何在CQRS模式中为Identity用户表触发领域事件？

我需要在身份事件（比如添加用户、使用UserManager操作）发生时触发领域事件，其他继承自BaseEntity的实体已经成功实现了这个功能，但我的ApplicationUser继承自IdentityUser，无法同时继承BaseEntity，请问该如何结合两者实现事件触发？

现有代码示例：

其他实体的实现（正常工作） #

public class Vehicle : BaseEntity
{
    // ... 实体属性
}

BaseEntity代码 #

public abstract class BaseEntity
{
    public string Id { get; set; }

    private readonly List<BaseEvent> _domainEvents = new();

    [NotMapped]
    public IReadOnlyCollection<BaseEvent> DomainEvents => _domainEvents.AsReadOnly();

    public void AddDomainEvent(BaseEvent domainEvent)
    {
        _domainEvents.Add(domainEvent);
    }

    public void RemoveDomainEvent(BaseEvent domainEvent)
    {
        _domainEvents.Remove(domainEvent);
    }

    public void ClearDomainEvents()
    {
        _domainEvents.Clear();
    }
}

无法实现的ApplicationUser #

public class ApplicationUser : IdentityUser
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string FatherName { get; set; }
}

由于C#不支持多继承，我们可以通过以下两种主流方案实现需求：

方案1：提取领域事件逻辑为独立类，通过组合复用 #

把BaseEntity中的领域事件管理逻辑封装成独立类，同时让BaseEntity和ApplicationUser都依赖这个类，既保证代码复用，又不破坏原有继承结构。

第一步：封装事件管理类 #

public class DomainEventCollection
{
    private readonly List<BaseEvent> _domainEvents = new();

    public IReadOnlyCollection<BaseEvent> DomainEvents => _domainEvents.AsReadOnly();

    public void AddDomainEvent(BaseEvent domainEvent)
    {
        _domainEvents.Add(domainEvent);
    }

    public void RemoveDomainEvent(BaseEvent domainEvent)
    {
        _domainEvents.Remove(domainEvent);
    }

    public void ClearDomainEvents()
    {
        _domainEvents.Clear();
    }
}

第二步：修改BaseEntity复用该类 #

public abstract class BaseEntity
{
    public string Id { get; set; }

    private readonly DomainEventCollection _eventCollection = new();

    [NotMapped]
    public IReadOnlyCollection<BaseEvent> DomainEvents => _eventCollection.DomainEvents;

    public void AddDomainEvent(BaseEvent domainEvent)
    {
        _eventCollection.AddDomainEvent(domainEvent);
    }

    public void RemoveDomainEvent(BaseEvent domainEvent)
    {
        _eventCollection.RemoveDomainEvent(domainEvent);
    }

    public void ClearDomainEvents()
    {
        _eventCollection.ClearDomainEvents();
    }
}

第三步：在ApplicationUser中集成事件管理类 #

public class ApplicationUser : IdentityUser
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string FatherName { get; set; }

    private readonly DomainEventCollection _eventCollection = new();

    [NotMapped]
    public IReadOnlyCollection<BaseEvent> DomainEvents => _eventCollection.DomainEvents;

    public void AddDomainEvent(BaseEvent domainEvent)
    {
        _eventCollection.AddDomainEvent(domainEvent);
    }

    public void RemoveDomainEvent(BaseEvent domainEvent)
    {
        _eventCollection.RemoveDomainEvent(domainEvent);
    }

    public void ClearDomainEvents()
    {
        _eventCollection.ClearDomainEvents();
    }
}

方案2：定义领域事件接口，让ApplicationUser实现接口 #

先抽离事件操作的标准接口，让BaseEntity和ApplicationUser分别实现该接口，后续可统一通过接口处理所有实体的领域事件。

第一步：定义事件接口 #

public interface IDomainEventEntity
{
    IReadOnlyCollection<BaseEvent> DomainEvents { get; }
    void AddDomainEvent(BaseEvent domainEvent);
    void RemoveDomainEvent(BaseEvent domainEvent);
    void ClearDomainEvents();
}

第二步：修改BaseEntity实现接口 #

public abstract class BaseEntity : IDomainEventEntity
{
    public string Id { get; set; }

    private readonly List<BaseEvent> _domainEvents = new();

    [NotMapped]
    public IReadOnlyCollection<BaseEvent> DomainEvents => _domainEvents.AsReadOnly();

    public void AddDomainEvent(BaseEvent domainEvent)
    {
        _domainEvents.Add(domainEvent);
    }

    public void RemoveDomainEvent(BaseEvent domainEvent)
    {
        _domainEvents.Remove(domainEvent);
    }

    public void ClearDomainEvents()
    {
        _domainEvents.Clear();
    }
}

第三步：让ApplicationUser实现接口 #

public class ApplicationUser : IdentityUser, IDomainEventEntity
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string FatherName { get; set; }

    private readonly List<BaseEvent> _domainEvents = new();

    [NotMapped]
    public IReadOnlyCollection<BaseEvent> DomainEvents => _domainEvents.AsReadOnly();

    public void AddDomainEvent(BaseEvent domainEvent)
    {
        _domainEvents.Add(domainEvent);
    }

    public void RemoveDomainEvent(BaseEvent domainEvent)
    {
        _domainEvents.Remove(domainEvent);
    }

    public void ClearDomainEvents()
    {
        _domainEvents.Clear();
    }
}

可以在UserManager操作完成后手动添加事件，或者自定义UserManager自动触发：

手动触发示例 #

var user = new ApplicationUser { /* 设置用户属性 */ };
var result = await _userManager.CreateAsync(user);
if (result.Succeeded)
{
    user.AddDomainEvent(new UserCreatedEvent(user.Id, user.Email));
    // 执行事件总线发布或其他处理逻辑
}

自定义UserManager自动触发 #

public class ApplicationUserManager : UserManager<ApplicationUser>
{
    public ApplicationUserManager(IUserStore<ApplicationUser> store, IOptions<IdentityOptions> optionsAccessor, IPasswordHasher<ApplicationUser> passwordHasher, IEnumerable<IUserValidator<ApplicationUser>> userValidators, IEnumerable<IPasswordValidator<ApplicationUser>> passwordValidators, ILookupNormalizer keyNormalizer, IdentityErrorDescriber errors, IServiceProvider services, ILogger<UserManager<ApplicationUser>> logger) 
        : base(store, optionsAccessor, passwordHasher, userValidators, passwordValidators, keyNormalizer, errors, services, logger)
    {
    }

    public override async Task<IdentityResult> CreateAsync(ApplicationUser user)
    {
        var result = await base.CreateAsync(user);
        if (result.Succeeded)
        {
            user.AddDomainEvent(new UserCreatedEvent(user.Id, user.Email));
        }
        return result;
    }
}

内容的提问来源于stack exchange，提问作者irancss