Cascade deleting with EntityFramework - entity-framework

Question

Have listed classes in model(simplified):
public partial class Category
{
public Category()
{
Topics = new HashSet<Topic>();
}
public Guid Id { get; set; }
public Guid? Category_Id { get; set; }//id for Parent category
public virtual ICollection<Topic> Topics { get; set; }
}
public partial class Topic
{
public Topic()
{
Posts = new HashSet<Post>();
}
public Guid Id { get; set; }
public string Name { get; set; }
public Guid Category_Id { get; set; }
public virtual ICollection<Post> Posts { get; set; }
public virtual Category Category { get; set; }
}
Model here:
public partial class EntityModel : DbContext
{
public EntityModel()
: base("name=EntityModelContext")
{
Configuration.LazyLoadingEnabled = true;
Configuration.AutoDetectChangesEnabled = true;
Debug.WriteLine("Context Created");
}
public virtual DbSet<Category> Category { get; set; }
public virtual DbSet<Post> Post { get; set; }
public virtual DbSet<Topic> Topic { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Category>()
.HasMany(e => e.Topics)
.WithRequired(e => e.Category)
.HasForeignKey(e => e.Category_Id)
.WillCascadeOnDelete(true);
modelBuilder.Entity<Topic>()
.HasMany(e => e.Posts)
.WithRequired(e => e.Topic)
.HasForeignKey(e => e.Topic_Id)
.WillCascadeOnDelete(true);
}
}
So problem:
when i trying to delete sub category (that have NOT NULL Category_Id) => delete successful, but when i need to delete root category(Category_Id = NULL) there is an exeption: The DELETE statement conflicted with the REFERENCE constraint “FK_Topic_Category”.
Yes, I can delete reffered topics in the root category before and then delete category. But want to know why in root case cascade delete not work.

Answer 1

ok, just added ON DELETE CASCADE to children entity's FK in DB annotation.