Beyond the Basics with Modeling and Inheritance - Entity Framework 6 Recipes - page 187

Listing 6-4. Creating the Product POCO Entity Class

[Table("Product", Schema = "Chapter6")]
public class Product
{
public Product()
{
RelatedProducts = new HashSet<Product>();
OtherRelatedProducts = new HashSet<Product>();
}

[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ProductId { get; set; }
public string Name { get; set; }
public decimal Price { get; set; }

// Products related to this product
public virtual ICollection<Product> RelatedProducts { get; set; }
// Products to which this product is related
public virtual ICollection<Product> OtherRelatedProducts { get; set; }
}

Add an auto-property of type DbSet<Product> to your DbContext subclass.

3.

Override the OnModelCreating method of DbContext in your subclass to create the
many-to-many self-referencing relationship mapping, as shown in Listing 6-5.

4.

Listing 6-5. Overriding OnModelCreating in the DbContext Subclass to Create the
Many-to-Many Self-Referencing Mapping

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);

modelBuilder.Entity<Product>()
.HasMany(p => p.RelatedProducts)
.WithMany(p => p.OtherRelatedProducts)
.Map(m =>
{
m.MapLeftKey("ProductId");
m.MapRightKey("RelatedProductId");
m.ToTable("RelatedProduct", "Chapter6");
});
}

How It Works
As you can see, the Entity Framework supports a many-to-many self-referencing association with little effort. We
created two navigation properties in our Product class, RelatedProducts and OtherRelatedProducts, and mapped
those properties to the underlying database schema in our DbContext subclass.