SQLite Entity Framework 查询 return 下一个可用日期

Question

我有这个查询从约会开始 table 我想获得该客户的下一个日期。

 from customer in db.Customers
 from order in db.Appointment
     .Where(o => customer.CustomerId == o.CustomerId)
     .DefaultIfEmpty()
Select new {NextAppointment = "How to get this date?"}

Class Appointment:

public class Appointment
{
    public long Id { get; set; }
    public string AppointmentInstructorName { get; set; }
    public DateTime LessonDate { get; set; }
   public long CustomerID {get; set;}
    public string AppointmentLessonAddress { get; set; }
}

Class Customer:

    public string FirstName;
    public string LastName;
    public string Suburb;
    public string NextAppointment;
    public string Mobile;
    public string DrivingLicenceNo;

    public string Name
    {
        get { return $"{FirstName} {LastName}"; }
    }

    public int ID;

当客户注册时，他们将获得与讲师上课的时间，在主页上，我想显示下一个可用预约

--更新--

这是我写的。这会影响性能还是应该没问题？仍然在寻找如何从约会中获得前 1 名 table

   var obj = (from a in Appointment
   orderby a.LessonDate ascending
   where a.LessonDate>= DateTime.Now
   select a);

   var d = (from c in Customer
   join o in obj on c.ID equals o.CustId into ps
   from o in ps.DefaultIfEmpty()
   select new { c, o.LessonDate});

Answer 1

得到它与这个一起工作：

var s = (from i in Customer
let p = Appointment.Where(p2 => i.ID == p2.CustId && p2.LessonDate >= DateTime.Now).OrderBy(ta => ta.LessonDate).FirstOrDefault()
select new
{
i, p.LessonDate
});

SQLite Entity Framework 查询 return 下一个可用日期

SQLite Entity Framework query to return next available date

sqlite

entity-framework

linq-to-sql