EF的lazyloading没起作用

Question

查询时，没有包含导航属性相关联的实体。这是什么情况？

根据某书教程例子写的代码：

实体：

public class PictureCategory
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int CategoryId { get; private set; }
        public string Name { get; set; }
        public int? ParentCategoryId { get; private set; }

        [ForeignKey("ParentCategoryId")]
        public PictureCategory ParentCategory { get; set; }

        public List<PictureCategory> Subcategories { get; set; }

        public PictureCategory()
        {
            Subcategories = new List<PictureCategory>();
        }
    }

关系：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            modelBuilder.Entity<PictureCategory>()
                       .HasMany(cat => cat.Subcategories)
                       .WithOptional(cat => cat.ParentCategory);

        }

运行：

public static void Run(){

 using (var context = new EF6Context())
            {
                context.Configuration.LazyLoadingEnabled = true;
                var roots = context.PictureCategories.Where(c => c.CategoryId ==1).ToList();
                roots.ForEach(root => Print(root, 0));
            }
        }

        public static void Print(PictureCategory cat, int level)
        {
            StringBuilder sb = new StringBuilder();
            Console.WriteLine("{0}{1}", sb.Append(' ', level).ToString(), cat.Name);
            cat.Subcategories.ForEach(child => Print(child, level + 1));
        }