INSERT语句与EF Core中的FOREIGN KEY约束冲突

关于这个错误在不同的上下文中有许多问题，到目前为止我还无法找到一个适用于我的情况的问题。

我有一个多对多的关系，我正试图建立第三个表。这基本上是一个人对管理者的联系。所有的经理都是人，但不是所有的人都是经理，而且，每个人都有很多经理，每个经理都有很多人。在经理表中是personid。在edit下的人员控制器中，有一个将人员与经理关联起来的选项。当单击可用的管理器并单击保存时，我得到错误:

INSERT语句与外键约束"FK_dbo.ManagerToEngineer_dbo.Manager_ManagerId"冲突。冲突发生在数据库"PROJECTNAME_16ce3f6a2a6c4ff0b1ce147d126984ba"，表"dbo"。Manager"，列"ManagerId"。语句已被终止。

SaveChanges方法导致以下错误:

        [HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult Edit(PersonViewModel person)
        {
            if (ModelState.IsValid)
            {
                //var MyPerson = db.people.Find(person.PersonId);
                //MyPerson.FirstName = person.FirstName;
                //MyPerson.LastName = person.LastName;
                foreach (var item in db.ManagersToEngineers)
                {
                    if (item.EngineerId == person.PersonId)
                    {
                        db.Entry(item).State = EntityState.Deleted;
                    }
                }
                foreach (var item in person.EngineerManagers)
                {
                    if (item.Checked)
                    {
                        db.ManagersToEngineers.Add(new ManagerToEngineer() { EngineerId = person.PersonId, ManagerId = item.Id });
                    }
                }
                //db.Entry(person).State = EntityState.Modified;
                db.SaveChanges();
                return RedirectToAction("Index");
            }
            return View(person);
        }

相关模型:

public class ManagerToEngineer
    {
        [Key]
        public int ManagerToEngineerId { get; set; }
        [Required]
        [ForeignKey("engineer")]
        public int EngineerId { get; set; }
        [Required]
        [ForeignKey("manager")]
        public int ManagerId { get; set; }
        public virtual Person engineer { get; set; }
        public virtual Manager manager { get; set; }
    }
public class Manager
{
    [Key]
    public int ManagerId { get; set; }
    [Required]
    [ForeignKey("person")]
    public int EngineerId { get; set; }
    public virtual Person person { get; set; }
    public ICollection<ManagerToEngineer> ManagersToEngineers { get; set; }
}
public class PersonViewModel
{
    public int PersonId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    [Display(Name = "Managers")]
    public List<CheckBoxViewModel> EngineerManagers { get; set; }
}
public class CheckBoxViewModel
{
    public int Id { get; set; }
    public string FullName { get; set; }
    public bool Checked { get; set; }
}

public class Person
{
    public Person()
    {
        Managers = new HashSet<Manager>();
    }
    [Key]
    public int PersonId { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Manager> Managers { get; set; }
}
public class Manager
{
    public Manager()
    {
        Persons = new HashSet<Person>();
    }
    [Key]
    public int ManagerId { get; set; }
    public virtual ICollection<Person> Persons { get; set; }
}
public class CompanyContext : DbContext
{
    public DbSet<Person> Persons { get; set; }
    public DbSet<Manager> Managers { get; set; }
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Person>()
           .HasMany(p => p.Managers).WithMany(m => m.Persons)
           .Map(t => t.MapLeftKey("PersonID")
               .MapRightKey("ManagerID")
               .ToTable("PersonToManager"));
    }
}

    static void Main(string[] args)
    {
        using (var db = new CompanyContext())
        {
            // add a person
            var person = new Person() { Name = "Joe" };
            db.Persons.Add(person);
            // "make" him manager
            var manager = new Manager();
            manager.Persons.Add(person);
            db.Managers.Add(manager);
            db.SaveChanges();
        }
        Console.ReadKey();
    }