基于MassTransit+Azure Service Bus，数据库更新后调用外部API发邮件咨询

1. 定义事件消息类（若未定义） #

首先确保UpdatedEventMessage已正确定义，用于传递注册编号：

public class UpdatedEventMessage
{
    public string RegistNumber { get; set; }
}

2. 创建事件消费者 #

实现MassTransit的IConsumer<UpdatedEventMessage>，整合数据库查询、外部API调用、邮件发送逻辑：

public class UpdatedEventConsumer : IConsumer<UpdatedEventMessage>
{
    private readonly AppDbContext _dbContext;
    private readonly ExternalUserApiClient _userApiClient;
    private readonly EmailService _emailService;

    // 通过依赖注入获取所需服务
    public UpdatedEventConsumer(AppDbContext dbContext, ExternalUserApiClient userApiClient, EmailService emailService)
    {
        _dbContext = dbContext;
        _userApiClient = userApiClient;
        _emailService = emailService;
    }

    public async Task Consume(ConsumeContext<UpdatedEventMessage> context)
    {
        var registNumber = context.Message.RegistNumber;

        // 步骤1：从本地数据库查询用户ID
        var userId = await _dbContext.Registrations
            .Where(r => r.RegistNumber == registNumber)
            .Select(r => r.UserId)
            .FirstOrDefaultAsync();

        if (userId == Guid.Empty)
        {
            await context.LogError($"未找到RegistNumber为{registNumber}的用户ID");
            return;
        }

        // 步骤2：调用外部API获取用户邮箱和称呼
        UserInfo userInfo;
        try
        {
            userInfo = await _userApiClient.GetUserInfoById(userId);
        }
        catch (HttpRequestException ex)
        {
            await context.LogError(ex, "调用外部用户API失败，用户ID：{UserId}", userId);
            return;
        }

        if (string.IsNullOrWhiteSpace(userInfo.Email))
        {
            await context.LogError("用户ID：{UserId}未配置邮箱地址", userId);
            return;
        }

        // 步骤3：发送通知邮件
        try
        {
            await _emailService.SendUpdateNotificationEmail(userInfo);
            await context.LogInformation("已成功向{Email}发送更新通知邮件", userInfo.Email);
        }
        catch (Exception ex)
        {
            await context.LogError(ex, "向{Email}发送邮件失败", userInfo.Email);
        }
    }
}

3. 实现本地数据库查询 #

使用EF Core实现从本地数据库获取用户ID的逻辑（假设你已有Registrations实体）：

// 数据库上下文示例
public class AppDbContext : DbContext
{
    public AppDbContext(DbContextOptions<AppDbContext> options) : base(options) { }

    public DbSet<Registration> Registrations { get; set; }
}

public class Registration
{
    public Guid Id { get; set; }
    public string RegistNumber { get; set; }
    public Guid UserId { get; set; }
    // 其他字段...
}

4. 实现外部API调用客户端 #

用HttpClient封装外部API调用，获取用户信息：

public class ExternalUserApiClient
{
    private readonly HttpClient _httpClient;

    public ExternalUserApiClient(HttpClient httpClient)
    {
        _httpClient = httpClient;
        // 从配置文件读取API地址，避免硬编码
        _httpClient.BaseAddress = new Uri(Environment.GetEnvironmentVariable("ExternalUserApiBaseUrl"));
    }

    public async Task<UserInfo> GetUserInfoById(Guid userId)
    {
        var response = await _httpClient.GetAsync($"api/users/{userId}");
        response.EnsureSuccessStatusCode(); // 非2xx状态码抛出异常

        return await response.Content.ReadFromJsonAsync<UserInfo>();
    }
}

// 外部API返回的用户信息模型
public class UserInfo
{
    public string Email { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

5. 实现邮件发送服务 #

用MailKit实现邮件发送（也可替换为SendGrid等服务）：

public class EmailService
{
    private readonly IConfiguration _configuration;

    public EmailService(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public async Task SendUpdateNotificationEmail(UserInfo userInfo)
    {
        using var smtpClient = new SmtpClient();
        // 从配置文件读取SMTP参数
        await smtpClient.ConnectAsync(
            _configuration["Smtp:Host"],
            int.Parse(_configuration["Smtp:Port"]),
            SecureSocketOptions.StartTls);
        
        await smtpClient.AuthenticateAsync(
            _configuration["Smtp:Username"],
            _configuration["Smtp:Password"]);

        var message = new MimeMessage();
        message.From.Add(new MailboxAddress("系统通知", _configuration["Smtp:FromEmail"]));
        message.To.Add(new MailboxAddress($"{userInfo.FirstName} {userInfo.LastName}", userInfo.Email));
        message.Subject = "您的注册信息已更新";

        message.Body = new TextPart("html")
        {
            Text = $@"
                <h3>您好，{userInfo.FirstName} {userInfo.LastName}:</h3>
                <p>您的注册信息已成功完成更新，如有疑问请联系客服。</p>
            "
        };

        await smtpClient.SendAsync(message);
        await smtpClient.DisconnectAsync(true);
    }
}

6. 配置MassTransit与Azure Service Bus #

在Program.cs中注册所有服务并配置MassTransit：

var builder = WebApplication.CreateBuilder(args);

// 注册数据库上下文
builder.Services.AddDbContext<AppDbContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));

// 注册外部API客户端
builder.Services.AddHttpClient<ExternalUserApiClient>();

// 注册邮件服务
builder.Services.AddTransient<EmailService>();

// 配置MassTransit和Azure Service Bus
builder.Services.AddMassTransit(x =>
{
    // 注册事件消费者
    x.AddConsumer<UpdatedEventConsumer>();

    x.UsingAzureServiceBus((context, cfg) =>
    {
        // 从配置文件读取Service Bus连接字符串
        cfg.Host(builder.Configuration["AzureServiceBus:ConnectionString"]);

        // 配置消费者接收端点
        cfg.ReceiveEndpoint("updated-event-email-handler", e =>
        {
            e.ConfigureConsumer<UpdatedEventConsumer>(context);

            // 配置重试策略：API调用或邮件发送失败时重试3次，间隔5秒
            e.UseMessageRetry(r => r.Interval(3, TimeSpan.FromSeconds(5)));

            // 配置死信队列：重试失败后将消息移入死信队列，避免重复消费
            e.DeadLetterQueueName = "updated-event-dead-letter";
        });
    });
});

var app = builder.Build();

// 其他中间件配置...

app.Run();

关键注意事项 #

• 错误处理：通过日志记录失败场景，利用MassTransit的重试和死信队列机制避免消息丢失
• 配置管理：所有敏感信息（连接字符串、API地址、SMTP参数）均从配置文件或环境变量读取，禁止硬编码
• 依赖注入：所有服务通过DI容器注入，保证代码可测试性和扩展性

内容的提问来源于stack exchange，提问作者Dhanyanjay Singh