Many-to-many relationship on the same table using a junction table and a primary key in EF

Question

I have the following tables:

• Sub_Option: Sub_Option_ID as PK, Name

• Sub_Option_To_Sub_Option: Sub_Option_To_Sub_Option_ID as PK, Sub_Option_ID_Primary, Sub_Option_ID_Secondary

I would like to be able to access all the secondary sub options associated with the primary sub option via EF and vice-versa. Directly using .Map won't work as the junction table Sub_Option_To_Sub_Option has a primary key.

public class Sub_Option
{
    public int Sub_Option_ID { get; set; }
    public string Name { get; set; }
}

corresponding to Table

CREATE TABLE Sub_Option(
Sub_Option_ID int,
Name varchar(255)
);

and Table

CREATE TABLE Sub_Option_To_Sub_Option(
Sub_Option_To_Sub_Option int PK, 
Sub_Option_ID_Primary int,
Sub_Option_ID_Secondary int
);

Answer 1

This should work i think:

    public class OptionToOption
{
    [Key]
    public int ID { get; set; }

    [ForeignKey("PrimaryOption")]
    public int PrimaryID { get; set; }

    [ForeignKey("SecondaryOption")]
    public int SecondaryID { get; set; }

    public virtual Option PrimaryOption { get; set; }

    public virtual Option SecondaryOption { get; set; }
}

    public class Option
{
    public Option()
    {
        OptionToOption = new HashSet<OptionToOption>();
    }

    [Key]
    public int ID { get; set; }

    public string Name { get; set; }

    public virtual ICollection<OptionToOption> OptionToOption { get; set; }
}

And in fluent api map like this (don't even think it's necessary to do this though):

            modelBuilder.Entity<Option>()
            .HasMany(e => e.OptionToOption)
            .WithRequired(e => e.PrimaryOption)
            .HasForeignKey(e => e.PrimaryID);

        modelBuilder.Entity<Option>()
            .HasMany(e => e.OptionToOption)
            .WithRequired(e => e.SecondaryOption)
            .HasForeignKey(e => e.SecondaryID);