how to do many to many with the same table with EF

Question

I have this schema:

create table Person
(
id int identity primary key,
name nvarchar(30)
)

create table PersonPersons
(
PersonId references Person(id),
ChildPersonId references Person(id)
)

how to create the classes to map them using EF4 Code First CTP5 ?

Answer 1

For the POCO...

class Person
{
    public Guid PersonId { get; set; }
    public virtual Person Parent { get; set; }
    public virtual ICollection<Person> Children { get; set; }
}

...set up the mapping in the DbContext...

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Person>()
        .HasOptional(entity => entity.Parent)
            .WithMany(parent => parent.Children)
            .HasForeignKey(parent => parent.PersonId);
}

...will give you a default implementation. If you need to rename the table explicitly (and want a many-to-many relationship), add in something like this...

class Person
{
    public Guid PersonId { get; set; }
    public virtual ICollection<Person> Parent { get; set; }
    public virtual ICollection<Person> Children { get; set; }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    ConfigureProducts(modelBuilder);
    ConfigureMembership(modelBuilder);

    modelBuilder.Entity<Person>()
        .HasMany(entity => entity.Children)
        .WithMany(child => child.Parent)
        .Map(map =>
        {
            map.ToTable("PersonPersons");
            map.MapLeftKey(left => left.PersonId, "PersonId"); 
            map.MapRightKey(right => right.PersonId, "ChildPersonId");
            // For EF5, comment the two above lines and uncomment the two below lines.
            // map.MapLeftKey("PersonId");
            // map.MapRightKey("ChildPersonId");
        }); 
}