Asp.Net mvc，如何制作异步和等待方法

Question

当需要下订单时，我会使用这两个操作向管理员发送有关库存状态的电子邮件... 但是当我打电话给 SendEmailToAdminUser .. 需要时间和并排我不能使用其他功能...等待很长时间.. 我想将这些功能更改为异步并等待任务......但我不知道该怎么做。我试图从 JsonResult 更改为 ActionResult ...

public JsonResult SendEmailToAdminUser()
{
    bool result = false;

    var emails = UserEmails();

    if (emails != null)
    {
        foreach (var email in emails)
        {
            var departmentId = context.Users.Where(e => e.Email == email)
                .Select(s => s.DepartmentId).FirstOrDefault();

            string departmentname = context.Departments.Where(u => u.deptId == departmentId)
                .Select(n => n.DepartmentName).Single();

            int[] ProductId = context.Inventory.Where(s => s.prId == departmentId)
                .Where(s => s.Status == 10).Select(s => s.PrId).ToArray();

            foreach (var product in ProductId)
            {
                string productname = context.Products.Where(n => n.prId == product)
                    .Select(n => n.ProductName).Single();

                result = SendEmail(email, productname, "<p> Hi there, <br />It is time to order " 
                    + productname + " to department: " + departmentname + "</p> <br /> /Regards");
            }
        }
    }

    return Json(result, JsonRequestBehavior.AllowGet)
}

而我的 SendEmail 功能是：

public bool SendEmail(string toEmail, string subject, string emailBody)
{
    try
    {
        string senderEmail = System.Configuration.ConfigurationManager.AppSettings["SenderEmail"].ToString();
        string senderPassword = System.Configuration.ConfigurationManager.AppSettings["SenderPassword"].ToString();

        SmtpClient client = new SmtpClient("smtp.gmail.com", 587);
        client.EnableSsl = true;
        client.Timeout = 100000;
        client.DeliveryMethod = SmtpDeliveryMethod.Network;
        client.UseDefaultCredentials = false;
        client.Credentials = new NetworkCredential(senderEmail, senderPassword);

        MailMessage mailMessage = new MailMessage(senderEmail, toEmail, subject, emailBody);
        mailMessage.IsBodyHtml = true;
        mailMessage.BodyEncoding = UTF8Encoding.UTF8;
        client.Send(mailMessage);

        return true;
    }
    catch(Exception ex)
    {
        return false;
    }
}

Answer 1

正如评论者所说，您不会从 async/await 中获得任何好处，因为您只会为其他请求释放底层线程。实际执行时间可能会长比您目前拥有的时间。

听起来您真正想要的是并发，可以使用Parallel.ForEach 轻松实现。但是，在使您的代码复杂化之前，我建议先进行一些更改。

• 重新使用SmtpClient 的实例。每次调用都需要实例化它，因为它每次都需要连接到后端 SMTP 服务。
• 正如 Shyju 指出的，优化您的算法。现在，您正在循环发送多封电子邮件到相同电子邮件地址。您可以将它们合并在一起，以尽量减少对SendMail 的调用量。
• 通过一次调用多个事物来最大限度地减少数据库调用次数。

根据您上面的代码：

public JsonResult SendEmailToAdminUser()
{
    bool result = false;

    var emails = UserEmails();

    if (emails != null)
    {
        // fetching data in batches
        var departmentIdsByEmail = context.Users
            .Where(x => emails.Contains(x.Email))
            .Select(x => new { x.Email, x.DepartmentId })
            .ToDictionary(x => x.Email, x => x.DepartmentId);

        var departmentIds = departmentIdsByEmail.Values;

        var departmentNamesById = context.Departments
            .Where(x => departmentIds.Contains(x.deptId))
            .ToDictionary(x => x.deptId, x => x.DepartmentName);

        var productNamesByDepartmentId = context.Inventory
            .Where(x => departmentIds.Contains(x.deptId))
            .Where(x => x.Status == 10)
            .GroupBy(x => x.deptId)
            .ToDictionary(g => g.Key, g => g.Select(x => x.Product.Name).ToArray());

        foreach (var emailWithDepartmentId in departmentIdsByEmail)
        {
            // send **one** email per address rather than many
            var email = emailWithDepartmentId.Key
            var departmentId = emailWithDepartmentId.Value;
            var departmentName = departmentNamesById[departmentId];
            var productNames = productNamesByDepartmentId[departmentId];

            result = SendEmail(
                email, 
                "<p> Hi there, <br />It is time to order "                      + string.Join(", ", productNames) + " to department: " + departmentName + "</p> <br /> /Regards");

        }
    }

    return Json(result, JsonRequestBehavior.AllowGet)
}

private static readonly SmtpClient _smtpClient = CreateSmtpClient();

private static SmtpClient CreateSmtpClient()
{
     string senderEmail = System.Configuration.ConfigurationManager.AppSettings["SenderEmail"].ToString();
     string senderPassword = System.Configuration.ConfigurationManager.AppSettings["SenderPassword"].ToString();

     SmtpClient client = new SmtpClient("smtp.gmail.com", 587);
     client.EnableSsl = true;
     client.Timeout = 100000;
     client.DeliveryMethod = SmtpDeliveryMethod.Network;
     client.UseDefaultCredentials = false;
     client.Credentials = new NetworkCredential(senderEmail, senderPassword);

     return client;
}

public bool SendEmail(string toEmail, string subject, string emailBody)
{
    string senderEmail = System.Configuration.ConfigurationManager.AppSettings["SenderEmail"].ToString();
    try
    {
        MailMessage mailMessage = new MailMessage(senderEmail, toEmail, subject, emailBody);
        mailMessage.IsBodyHtml = true;
        mailMessage.BodyEncoding = UTF8Encoding.UTF8;
        _smtpClient.Send(mailMessage);

        return true;
    }
    catch(Exception ex)
    {
        return false;
    }
}

这些内容相当统一，但希望能给你一个开始。本质上，您只需要尽量减少您正在执行的 I/O 数量，您应该会看到显着的性能提升！