自连接<EntityFramework6.0>

 public class PictureCategory    {        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]        public int CategoryId { get; PRivate set; }        public string Name { get; set; }        public int? ParentCategoryId { get; private set; }        public virtual PictureCategory ParentCategory { get; set; }        public virtual ICollection<PictureCategory> SubPictureCategories { get; set; }        public PictureCategory()        {            SubPictureCategories = new HashSet<PictureCategory>();        }    }    public class PictureCategoryContext : DbContext    {        public virtual DbSet<PictureCategory> PictureCategories { get; set; }        public PictureCategoryContext() : base("name=DemoContext") { }        protected override void OnModelCreating(DbModelBuilder modelBuilder)        {            base.OnModelCreating(modelBuilder);            modelBuilder.Entity<PictureCategory>()                .HasKey(p=>p.CategoryId)                .HasMany(p => p.SubPictureCategories)                .WithOptional(t => t.ParentCategory)                .HasForeignKey(t=>t.ParentCategoryId);        }    }

private static void Main()        {            using (var context = new PictureCategoryContext())            {                var _1st = new PictureCategory { Name = "第1代" };                var _2st = new PictureCategory { Name = "第2代" };                var _3_1st = new PictureCategory { Name = "第3_1代" };                var _3_2st = new PictureCategory { Name = "第3_2代" };                var _3_3st = new PictureCategory { Name = "第3_3代" };                var _4st = new PictureCategory { Name = "第4代" };                var _5_1st = new PictureCategory { Name = "第5_5_1代" };                var _5_2st = new PictureCategory { Name = "第5_2代" };                _1st.SubPictureCategories = new List<PictureCategory> { _2st };                _2st.SubPictureCategories = new List<PictureCategory> { _3_1st, _3_2st, _3_3st };                _3_3st.SubPictureCategories = new List<PictureCategory> { _4st };                _4st.SubPictureCategories = new List<PictureCategory> { _5_1st, _5_2st };                context.PictureCategories.Add(_1st);                context.SaveChanges();            }            using (var context=new PictureCategoryContext())            {               var query = context.PictureCategories.Where(p=>p.ParentCategory==null).ToList();               query.ForEach(t => Print(t,1));            }            Console.ReadKey();        }        private static void Print(PictureCategory category, int level)        {            Console.WriteLine("{0}--{1}", category.Name, level);            category.SubPictureCategories.ToList().ForEach(t=>Print(t,level+1));        }