Question

I have the code as below.

  class Student : IPeople
{
    private string name;
    public string Name
    {
        get { return name;}
        set { name = value;}
    }

    private bool sex;
    public bool Sex
    {
        get{ return sex; }
        set{ sex = value;}
    }

    private int age;
    public int Age
    {
        get{return age;}
        set{age = value;}
    }

    public virtual ICollection<Dog> dogs { get;set; }

    public Student()
    {
        dogs = new List<Dog>();
    }
}

class Pet
{
    string Name { get; set; }
    bool Sex { get; set; }
    int Age{get;set;}
}

class Dog : Pet
{
    public string Type { get; set; }
    public virtual ICollection<IPeople> persons { get; set; }

    public Dog()
    {
        persons = new List<IPeople>();
    }
}

The context is

class TestContext : DbContext
{
    public DbSet<Student> studentSet { get; set; }
    public DbSet<Dog> dogSet { get; set; }
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Student>().HasMany(x => x.dogs).WithMany(y => (ICollection<Student>)y.persons);
    }
}

If I insert the records likes below,

using (TestContext context = new TestContext())
        {
            Student s = new Student();
            s.Age = 18;
            s.Sex = true;
            s.Name = "ts";
            Dog d = new Dog();
            d.Type = "abc";
            d.Sex = false;
            d.Name = "dog";
            d.Age = 3;
            s.dogs.Add(d);
            context.studentSet.Add(s);
            context.SaveChanges();
        }

everything works well, but if I insert the records likes below, the Student record will not insert into database.

using (TestContext context = new TestContext())
        {
            Student s = new Student();
            s.Age = 18;
            s.Sex = true;
            s.Name = "ts";
            Dog d = new Dog();
            d.Type = "abc";
            d.Sex = false;
            d.Name = "dog";
            d.Age = 3;
            d.persons.Add(s);
            context.dogSet.Add(d);
            context.SaveChanges();
        }

Anyone can help?

Answer 1

You can’t use the interface IPeople here:

public virtual ICollection<IPeople> persons { get; set; }

Navigation properties must refer to entity classes – either abstract or concrete – of your model.

A possible alternative might be to use an abstract class People instead of an interface. But you have to put the navigation property…

public virtual ICollection<Dog> dogs { get;set; }

…into that abstract class, not into the derived Student class, because Dog.persons refers to the abstract class People, something like:

abstract class People
{
    // ...
    public virtual ICollection<Dog> dogs { get;set; }
}

class Student : People
{
    // ...
}

class Pet
{
    // ...
}

class Dog : Pet
{
    // ...
    public virtual ICollection<People> persons { get; set; }
}

And the mapping would be:

modelBuilder.Entity<People>()
    .HasMany(x => x.dogs)
    .WithMany(y => y.persons)
    .Map(m =>
    {
        m.ToTable("PeoplesDogs");
        m.MapLeftKey("PeopleId");
        m.MapRightKey("DogId");
    });