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首页 > 解决方案 > 'await' 运算符只能在异步 lambda 表达式中使用。考虑用 'async' 修饰符标记这个 lambda 表达式

c# - 'await' 运算符只能在异步 lambda 表达式中使用。考虑用 'async' 修饰符标记这个 lambda 表达式

问题描述

在以下 LinQ 查询以获取电话号码时，我正在调用另一个异步方法 GetAspNetUserPhoneNumberByAccountId，这会引发此错误

错误 CS4034 'await' 运算符只能在异步 lambda 表达式中使用。考虑用 'async' 修饰符标记这个 lambda 表达式。

有人知道吗？

 var fullAppointment = await Task.Run(() => Context.AppointmentDetail
     .Where(u =>
     u.StartDateTime >= startdatetime
      && u.EndDateTime <= enddatetime

      )
       .Select(x => new Contracts.CalenderModel2()
        {
          StatusId = (Contracts.Enum.EnumWOStatus)x.Status,
          FName = x.Appointment != null ? x.Appointment.Customer.Account.FName : "",
          LName = x.Appointment != null ? x.Appointment.Customer.Account.LName : "",
          **PrimaryPhone = x.Appointment != null ?
          (await _userRepository.GetAspNetUserPhoneNumberByAccountId( x.Appointment.Customer.AccountId))**
          : "",
          Year = x.Appointment != null && x.Appointment.Vehicle != null ? x.Appointment.Vehicle.MakeYear.Year : 0,
          Make = x.Appointment != null && x.Appointment.Vehicle != null ? x.Appointment.Vehicle.VehicleMaker.MakerName : "",
          Model = x.Appointment != null && x.Appointment.Vehicle != null ? x.Appointment.Vehicle.VehicleModel.Model : "",
          AppointmentId = x.AppointmentId,
          JobEndDateTime = x.EndDateTime,
          JobStartDateTime = x.StartDateTime,
          ColorCategory = x.AppointmentType.ColorCategory,

          SalesRepersentativeUserId =
(x.Appointment != null && x.Appointment.Customer.CustomerBillTo.Count > 0)
              ? x.Appointment.Customer.CustomerBillTo.FirstOrDefault().BillToId : Guid.Empty,

          FullAppointmentDetail = new Contracts.FullAppointmentDetail
          {
            BayId = x.BayId,
            BayName = x.WorkArea != null ? x.WorkArea.BayName : "",
            WorkTypeId = x.WorkTypeId,
            WorkTypeName = x.WorkType != null ? x.WorkType.WorkTypeName : "",
            JobId = x.Appointment != null && x.Appointment.Job != null ? x.Appointment.Job.Id : Guid.Empty,
            JobIdInt = x.Appointment != null && x.Appointment.Job != null ? x.Appointment.Job.JobIdInt : 0,
            AssigneeUserId = x.AssigneeUserId,
            WorkOrderId = x.WorkOrders.FirstOrDefault() != null ? x.WorkOrders.FirstOrDefault().Id : Guid.Empty
          }

        })
        .ToList());

GetAspNetUserPhoneNumberByAccountId 的定义如下

public async Task<string> GetAspNetUserPhoneNumberByAccountId(Guid accountId)
{
  var phone = await Task.Run(() => _Context.Account.Where(ac => ac.Id.Equals(accountId))
   .Join(_Context.AspNetUsers, ac => ac.AspNetUserId, u => u.Id, (ac, u) => new 
   {
     PhoneNumber = u.PhoneNumber,

   }).FirstOrDefault());

  return phone!=null?phone.ToString():"";
}

标签： c#entity-frameworklinq

解决方案

我同意评论中的人的观点，即您不需要在此查询中使用异步方法。此外，此查询不会优化。对于 Where 条件中的每个项目，您将查询到 DB。如果你有很多数据，数据库的性能会下降。我认为在这种情况下对数据库进行 2 次查询要好得多。获取AppointmentDetail和获取所有帐户的另一个查询。并且两个查询调用都是异步的。然后将它结合到你的Contracts.CalenderModel2课程中。

它将更具可读性并且工作得更快。并且不要使用 Task.Run();

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