如何使用 Entity Framework 保存多对多关系

Question

嗨，我在 Flight 和 Journey 之间有很多关系，所以我创建了一个中间表来创建关系：

问题是，我有一个航班列表和一个旅程，那么我如何创建代码来制作程序集，以便在使用实体框架保存它之后？

创建模型和上下文，此代码似乎没问题：

//process to create the Flight with the Transport list

 var journey = new Journey()

{

                    JourneyOrigin = origin,

                    JourneyDestination = destination,

                    JourneyPrice = SumPrice

};


var response = new JourneyFlight()

{

                    Journey = journey,

                    Flight = flights[0]

};


            

Note：此问题总结整理于:How to save a many to many relationship with Entity Framework

Answer 1

欢迎来到 Microsoft Q&A，如果要在 ef core 中保存多对多关系，建议先使用代码生成模型，并在 OnModelCreating 事件中定义一些关系。

下面是一个可以参考的代码示例。

模型和 Dbcontext：

public class JourneyFlight
    {
        public int JourneyFlightId { get; set; }

        public int JourneyId { get; set; }
        public int FlightId { get; set; }

        public Journey? journey { get; set; }

        public Flight? flight { get; set; }


    }

    public class Journey
    {
        public int JourneyId { get; set; }

        public double JourneyPrice { get; set; }

        public ICollection<JourneyFlight>? journeyFlights { get; set; }
    }
    public class Flight
    {
        public int FlightId { get; set; }
        public double FlightPrice { get; set;}

        public int TransportId { get; set; }
        public Transport? transport { get; set; }
        public ICollection<JourneyFlight>? journeyFlights { get; set; }
    }

    public class Transport
    {
        public int TransportId { get; set; }

        public int TransportFlightNumber { get; set; }

        public ICollection<Flight>? flights;
    }

    public class MyContext:DbContext
    {
        public DbSet<JourneyFlight> journeyFlights { get; set; }

        public DbSet<Journey> journeys { get; set; }

        public DbSet<Flight> flights { get; set; }

        public DbSet<Transport> transports { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer("connstr");
        }
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<JourneyFlight>().HasKey(m => new { m.JourneyId, m.FlightId });
            modelBuilder.Entity<JourneyFlight>().HasOne(m => m.journey).WithMany(m => m.journeyFlights).HasForeignKey(m=>m.JourneyId);
            modelBuilder.Entity<JourneyFlight>().HasOne(m => m.flight).WithMany(m => m.journeyFlights).HasForeignKey(m=>m.FlightId);
            modelBuilder.Entity<Flight>().HasOne(m => m.transport).WithMany(m => m.flights).HasForeignKey(m => m.TransportId);

        }
    } 

如何在main方法中添加数据：

MyContext context=new MyContext();
           JourneyFlight journeyFlight1=new JourneyFlight();
            JourneyFlight journeyFlight2 = new JourneyFlight();
            var j1=new Journey();
            j1.JourneyPrice = 100;
            var j2=new Journey();
            j2.JourneyPrice = 200; 
            var f1=new Flight();
            f1.FlightPrice = 50;
            var f2=new Flight();    
            f2.FlightPrice = 70;
            journeyFlight1.journey = j1;
            journeyFlight1.flight = f1;
            journeyFlight2.journey = j2;
            journeyFlight2.flight = f2;
            Transport transport = new Transport();
            transport.flights = new List<Flight>
            {
                f1,
                f2
            };
            transport.TransportFlightNumber = 1001;
            context.journeyFlights.Add(journeyFlight1);
            context.journeyFlights.Add(journeyFlight2);
            context.transports.Add(transport);
            context.SaveChanges();

根据我的测试，我可以在sql server中得到以下结果：

希望我的代码示例能对您有所帮助。

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