LINQ to Entities外鍵協會

Question

我是新來的asp.net，C＃和SQL，可以使用一些指導..我使用：下面：數據庫與linq實體框架。我需要將特定的「乘車」與特定的「車輛」相關聯，但我不確定如何繼續。我已經在兩個物體之間設置了導航屬性，但是現在需要讓車輛持有對其所乘坐的列表的引用。我需要一個單獨的車輛列來保存這個列表嗎？有人可以告訴我完成這個的語法嗎？

這裏是我目前擁有的代碼，並在兩個點意見，我需要幫助：

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

爲：

// 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實體有Rides集合屬性已經根據到你的模型圖，所以你應該只能夠說：

assignedCar.Rides.Add(newRide); 

最後 - 純粹是個人喜好的問題 - 而不是：

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

我會使用：

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

Answer 2

在我看來，下面的文章是很好的起點：

1. EF 4.1 Code First Walkthrough
2. Code First Relationships Fluent API。請參閱博客和博客實體，其中博客有一個一對多 關係與帖子。