LINQ to Entities外键协会

Question

我是新来的asp.net，C＃和SQL，可以使用一些指导..我使用：下面：数据库与linq实体框架。我需要将特定的“乘车”与特定的“车辆”相关联，但我不确定如何继续。我已经在两个物体之间设置了导航属性，但是现在需要让车辆持有对其所乘坐的列表的引用。我需要一个单独的车辆列来保存这个列表吗？有人可以告诉我完成这个的语法吗？

这里是我目前拥有的代码，并在两个点意见，我需要帮助：

private void setNewRide(Ride newRide, int carNum) 
     { 
      using (myEntities = new RamRideOpsEntities()) 
      { 
       var assignedCar = (from car in myEntities.Vehicles 
           where (car.CarNum == carNum) 
           select car).FirstOrDefault(); 

       if (assignedCar != null && newRide != null) 
       {     

        Ride lastRide = assignedCar.Rides.LastOrDefault(); //HERE IS WHERE I NEED TO LOAD THE MOST RECENT 'RIDE' FOR THIS CAR, IS THIS CORRECT??? 

        if (lastRide != null) 
        { 
         lastRide.Status = "Completed"; 
         assignedCar.numRides = assignedCar.numRides + 1; 
         lastRide.TimeDroppedOff = DateTime.Now; 
         TimeSpan duration = (lastRide.TimeDroppedOff - lastRide.TimeDispatched).Value; 

         lastRide.ServiceTime = duration; 
         if (assignedCar.AvgRideTime == null) 
         { 
          assignedCar.AvgRideTime = duration; 
         } 
         else 
         { 
          assignedCar.AvgRideTime = TimeSpan.FromSeconds((((TimeSpan)assignedCar.AvgRideTime).Seconds + duration.Seconds)/assignedCar.numRides); 
         } 
        } 

        assignedCar.Status = "EnRoute"; 
        assignedCar.CurrPassengers = newRide.NumPatrons; 
        assignedCar.StartAdd = newRide.PickupAddress; 
        assignedCar.EndAdd = newRide.DropoffAddress; 

        //HERE IS WHERE I NEED TO ADD THE 'newRide' OBJECT TO THE LIST OF RIDES IN THE 'assignedCar' ..SYNTAX??? 

        newRide.TimeDispatched = DateTime.Now; 
        newRide.AssignedCar = carNum; 
        newRide.Status = "EnRoute"; 

        myEntities.SaveChanges(); 
        SelectCarUP.DataBind(); 
        SelectCarUP.Update();      
       } 
      } 
     } 

Answer 1

为：

// HERE IS WHERE I NEED TO LOAD THE MOST RECENT 'RIDE' FOR THIS CAR, IS 
// THIS CORRECT??? 
Ride lastRide = assignedCar.Rides.LastOrDefault(); 

用途：

Ride lastRide = assignedCar.Rides 
    .OrderByDescending(r => r.TimeDispatched) 
    .FirstOrDefault(); 

...和：

// HERE IS WHERE I NEED TO ADD THE 'newRide' OBJECT TO THE LIST OF RIDES 
// IN THE 'assignedCar' ..SYNTAX??? 

...你Vehicle实体有Rides集合属性已经根据到你的模型图，所以你应该只能够说：

assignedCar.Rides.Add(newRide); 

最后 - 纯粹是个人喜好的问题 - 而不是：

var assignedCar = (from car in myEntities.Vehicles 
        where (car.CarNum == carNum) 
        select car).FirstOrDefault(); 

我会使用：

var assignedCar = myEntities.Vehicles 
    .FirstOrDefault(car => car.CarNum == carNum); 

Answer 2

在我看来，下面的文章是很好的起点：

1. EF 4.1 Code First Walkthrough
2. Code First Relationships Fluent API。请参阅博客和博客实体，其中博客有一个一对多 关系与帖子。