mbdavid/LiteDB

Second question: about DbRef
Here, I have this model

public class CategoryModel : BaseLiteDBModel
    {
        public new static readonly string CollectionName = "categories";

        public int CategoryID { get; set; }
        public string CategoryName { get; set; }
        public int? OrderNumber { get; set; }
        public int BooksCount { get; set; }
        public int? ParentCategoryID { get; set; }

        public virtual CategoryModel ParentCategory { get; set; }

        public CategoryModel()
        {
        }

        [BsonCtor]
        public CategoryModel(int categoryID, string categoryName, int? orderNumber, int booksCount, int? parentCategoryID, CategoryModel parentCategory)
        {
            CategoryID = categoryID;
            CategoryName = categoryName;
            OrderNumber = orderNumber;
            BooksCount = booksCount;
            ParentCategoryID = parentCategoryID;
            ParentCategory = parentCategory;
        }

        internal static void MappingInit()
        {
            BsonMapper.Global.Entity<CategoryModel>()
                //.Ctor(/**/)
                .Id(x => x.CategoryID, true)
                .Field(x => x.CategoryName, "CategoryName")
                .Field(x => x.OrderNumber, "OrderNumber")
                .Field(x => x.ParentCategoryID, "ParentCategoryID")
                .Ignore(x => x.BooksCount)
                .DbRef(x => x.ParentCategory);
        }
    }

and I did these insertions

Collection.Insert(new CategoryModel
            {
                CategoryName = "Category 1",  // Auto id will be : 1
            });
Collection.Insert(new CategoryModel
            {
                CategoryName = "Category 2",
            });
Collection.Insert(new CategoryModel
            {
                CategoryName = "Category 3",
                                ParentCategoryID = 1,
            });

then tried to retrieve them with include but ParentCategory is always null , what's wrong?

Collection.Include(x => x.ParentCategory).Query().ToList();