如何向 LlNQ where 子句添加 2 个以上条件？

Question

我有一个包含超过 2 个 where 条件的 LINQ 查询，但它似乎无法使用超过 2 个条件进行评估。有没有办法向 where 子句添加更多条件？

var query = 
   from f in XElement.Load(MapPath("flightdata3.xml")).Elements("flight")
   where (string)f.Element("departurelocation") == From && 
         (string)f.Element("destinationlocation") == DestCity &&
         (string)f.Element("airline") == Airline
         // && (string)f.Element("departuredate") == DepartDate && 
         // (string)f.Element("departuretime")==DepartTime
         //&& (string)f.Element("returndate")==ReturnDate && 
         //(string)f.Element("returntime")==ReturnTime
   orderby Convert.ToInt32(f.Element("price").Value)
   select new
   {
      FlightNumber = (Int32)f.Element("flightnumber"),
      Airline = (string)f.Element("airline"),
      Departure = (string)f.Element("departureairportsymbol"),
      DepartTime = (string)f.Element("departuretime"),
      Destination = (string)f.Element("destinationairportsymbol"),
      ArrivalTime = (string)f.Element("arrivaltime"),
      Stops = (int)f.Element("numberofstops"),
      Duration = (string)f.Element("duration"),
      Cabin = (string)f.Element("cabin"),
      Price = "$" + (Int32)f.Element("price"),
      ImagePath = (string)f.Element("airlineimageurl").Value
   };

Answer 1

拥有多个条件应该没有问题。例如，您可以从订单表中获得类似的内容。

var orderDetails = (from o in context.OrderDetails
where o.OrderID == orderID
where o.OrderName == orderName
select o).ToList();

Answer 2

LINQ 绝对允许两个以上的 WHERE 条件。您是否尝试过将查询分成更易于管理的部分？无论如何，LINQ 使用延迟执行，因此您不会看到这样做会造成性能损失。

您还应该考虑创建一个类来保存您要填充到结果中的信息。

public class FlightDetail
{
    public Int32 FlightNumber { get; set; }

    public String Airline { get; set; }

    public String Departure { get; set; }

    public String DepartureTime { get; set; }

    public String Destination { get; set; }

    public String ArrivalTime { get; set; }

    public Int32 Stops { get; set; }

    public String Duration { get; set; }

    public String Cabin { get; set; }

    public Int32 Price { get; set; }

    public String ImagePath { get; set; }
}

然后是这样的东西，它更具可读性，但也应该帮助您找到出现的任何错误。

var flights = 
   from f in XElement.Load(MapPath("flightdata3.xml")).Elements("flight")
   select new FlightDetail
   {
      FlightNumber = (Int32)f.Element("flightnumber"),
      Airline = (string)f.Element("airline"),
      Departure = (string)f.Element("departureairportsymbol"),
      DepartTime = (string)f.Element("departuretime"),
      Destination = (string)f.Element("destinationairportsymbol"),
      ArrivalTime = (string)f.Element("arrivaltime"),
      Stops = (int)f.Element("numberofstops"),
      Duration = (string)f.Element("duration"),
      Cabin = (string)f.Element("cabin"),
      Price = "$" + (Int32)f.Element("price"),
      ImagePath = (string)f.Element("airlineimageurl").Value
   };

var flightsByLocation = 
   flights.
   where (string)f.Element("departurelocation") == From && 
         (string)f.Element("destinationlocation") == DestCity
   select new FlightDetail
   {
      FlightNumber = (Int32)f.Element("flightnumber"),
      Airline = (string)f.Element("airline"),
      Departure = (string)f.Element("departureairportsymbol"),
      DepartTime = (string)f.Element("departuretime"),
      Destination = (string)f.Element("destinationairportsymbol"),
      ArrivalTime = (string)f.Element("arrivaltime"),
      Stops = (int)f.Element("numberofstops"),
      Duration = (string)f.Element("duration"),
      Cabin = (string)f.Element("cabin"),
      Price = "$" + (Int32)f.Element("price"),
      ImagePath = (string)f.Element("airlineimageurl").Value
   };