c# - 在 LINQ 中使用 IN 运算符

Question

我有 List<Candidate> Candidates, List<Seat> Seats

Model定义如下图

 public class Seat
    {

         public string CollegeId { get; set; }
         public bool isFilled { get; set; }
         public string SeatType { get; set; }
         public string RollNumber { get; set; }
    }
     public class Candidate
     {
         public string RollNumber { get; set; }
         public bool isAllotted { get; set; }
         public string Quota { get; set; }
         public int CandidateRank { get; set; }
         public List<OptionPriority> SeatingPriorities { get; set; }

     }
     public class OptionPriority
     {
         public string CollegeId { get; set; }
         public int PriorityRank { get; set; }
     }

我需要过滤 List<Seat>来自 List<Seat> Seats其中 Seats.CollegeId在 SeatingPriorities 中的 CollegeID 列表中。

Answer 1

// same as EXISTS
Seats.Where(s => SeatingPriorities.Any(sp => sp.CollegeId == s.CollegeId))

您还可以加入具有座位优先级的座位:

// same as INNER JOIN
var prioritySeats = from s in Seats
                    join sp in SeatingPriorities
                         on s.CollegeId equals sp.CollegeId
                    select s;

注意:如果您将在 LINQ to SQL 或 LINQ to Entities 中执行上述两个查询，它们将不会生成 IN 子句。当您使用原始类型列表的 Contains 方法时生成 IN:

var ids = SeatingPriorities.Select(sp => sp.CollegeId).ToList();
// same as IN
var prioritySeats = Seats.Where(s => ids.Contains(s.CollegeId));