EF Core 多对多不保存到连接 table

Question

我有以下类

public class Travel
{
    public int Id { get; set; }
    public string Location { get; set; }
    public DateTime StartDate { get; set; }
    public DateTime EndDate { get; set; }
    public List<Activity> Activities { get; set; }
    public List<ActivityTravel> ActivitityTravels { get; set; } = new List<ActivityTravel>();
}

public class Activity
{
    public int Id { get; set; }
    public string Name { get; set; }
    public List<ActivityTravel> ActivitityTravels { get; set; } = new List<ActivityTravel>();
}

public class ActivityTravel
{
    public int TravelId { get; set; }
    public Travel Travel { get; set; }
    public int ActivityId { get; set; }
    public Activity Activity { get; set; }
}

我的 ApplicationDbContext 看起来像这样

modelBuilder.Entity<ActivityTravel>()
        .HasKey(at => new { at.ActivityId, at.TravelId });

        modelBuilder.Entity<ActivityTravel>()
        .HasOne(at => at.Activity)
        .WithMany(a => a.ActivitityTravels)
        .HasForeignKey(at => at.ActivityId);

        modelBuilder.Entity<ActivityTravel>()
        .HasOne(at => at.Travel)
        .WithMany(t => t.ActivitityTravels)
        .HasForeignKey(at => at.TravelId);

    //outside of OnModelCreating
    public DbSet<Travel> Travels { get; set; }
    public DbSet<Activity> Activities { get; set; }
    public DbSet<ActivityTravel> ActivityTravels { get; set; }

用户可以添加一个新的 Travel 以及一些已经存在的 Activites。但是每次将新的 Travel 添加到上下文中时，ActivityTravel 中不会添加任何内容。这是用于添加新的 Travel

的代码

    public async Task<ActionResult> AddTravel([FromBody] Travel travel)
    {   
        travel.Activities.ForEach(a => travel.ActivitityTravels.Add(new ActivityTravel() { Activity = a, Travel = travel }));
        _context.Travels.Add(travel);

        //dont add activity again
        travel.Activities.ForEach(a => _context.Entry(a).State = EntityState.Detached);
        _context.SaveChanges();

        return Ok();
    }

我已经按照这个问题中的例子做了

Answer 1

你不应该分离你现有的 Activities 你需要先 attach 它们再处理其他东西，这样它们就不会被添加为重复项。像这样：

public async Task<ActionResult> AddTravel([FromBody] Travel travel)
{   
    travel.Activities.ForEach(a => travel.ActivitityTravels.Add(new ActivityTravel() { Activity = a, Travel = travel }));
    _context.AttachRange(travel.Activities);
    _context.Travels.Add(travel);
    _context.SaveChanges();
    return Ok();
}

EF Core 多对多不保存到连接 table

EF Core many to many not saving into join table

c#

many-to-many

entity-framework

.net-core