无法在 razor 上使用外键对空引用执行运行时绑定

Question

这是我的模型

public class Appointment
{
    public int id { get; set; }
    public DateTime start { get; set; }
    public DateTime end { get; set; }
    public Patient patient { get; set; }
    ...
}
...
public class Patient
{
    public int id { get; set; }
    public string cin { get; set; }
    public string name { get; set; }
    public User doctor { get; set; }
}

我正在尝试在剃刀中显示每个医生预约的患者姓名

foreach (var appointment in date)
{
    <tr>
        <td>@appointment.patient.name</td>
    </tr>
}

但我收到此错误：

无法对空引用执行运行时绑定

它适用于所有其他属性（id、start、end）但不适用于患者，这是一个外键

更新

这是返回约会的函数

public dynamic appointments()
{
    Database db = new Database();
    var query = db.Appointments.Where(a => a.patient.doctor == this).AsEnumerable().GroupBy(a => a.start.Date);
    var appointments = query.ToList();
    return appointments;
}

约会按每个日期分组，这就是它们在视图中的显示方式

foreach (var date in ViewBag.Appointments)
@{
    <h3><b>@date.Key.ToString("dd/MM/yyyy")</b></h3>
    <table>
        foreach (var appointment in date)
        @{
            <tr>
                <td>@appointment.patient.name</td>
            </tr>
        }
    </table>
}

Answer 1

尝试修复您的模型

public class Appointment
{
    public int id { get; set; }
   ....
     public int? patientId { get; set; }
    public virtual Patient patient { get; set; }
    ...
}

public class Patient
{
    public int id { get; set; }
     ....
      public int? doctorId { get; set; }
      public virtual User doctor { get; set; }

    public virtual ICollection<Appointment> appointments { get; set; }

}

并获得约会

public List<Appointment> appointments()
{
    Database db = new Database();
   return = db.Appointments
         .Include(p=> p.Patient)
         .Where(a => a.patient.doctorId == doctorId)
                  //or maybe a.patient.doctorId == this.doctorId I don't 
                    know what is "this"
          .GroupBy(a => a.start.Date)
          .ToList();
 
}

但我认为将 PatientName 属性添加到 Appointment 会更有效

[NotMapped]
public string PatientName {get; set;}

在这种情况下，您不需要返回整个 Patient 类

var appointments = db.Appointments
         .Include(p=> p.Patient)
         .Where(a => a.patient.doctorId == doctorId)
                  //or maybe a.patient.doctorId == this.doctorId I don't 
                    know what is "this"
          .GroupBy(a => a.start.Date)
          .ToList();

  foreach( var i=0; i< appointments.Count; i+=1)
{
     appointment[i].PatientName=list[i].Patient.Name;
     appointment[i].Patient=null;
}
 return appointements;

或者也许只是这个：

public List<string> appointmentNames()
{
    Database db = new Database();
   return = db.Appointments
           .Where(a => a.patient.doctorId == doctorId)
                  //or maybe a.patient.doctorId == this.doctorId I don't 
                    know what is "this"
          .GroupBy(a => a.start.Date)
          .Select (a=> a.Patient.Name)
          .ToList();
 
}