protected override void Initialize()
        {
            var ed1 = new BiRefEdEntity {
                Id = 1, Data = "data_ed_1"
            };
            var ed2 = new BiRefEdEntity {
                Id = 2, Data = "data_ed_2"
            };
            var ing1 = new BiRefIngEntity {
                Id = 3, Data = "data_ing_1"
            };

            using (var tx = Session.BeginTransaction())
            {
                ing1.Reference = ed1;
                ed1_id         = (int)Session.Save(ed1);
                ed2_id         = (int)Session.Save(ed2);
                ing1_id        = (int)Session.Save(ing1);
                tx.Commit();
            }
            using (var tx = Session.BeginTransaction())
            {
                ing1.Reference = ed2;
                tx.Commit();
            }
        }
        protected override void Initialize()
        {
            var ed1 = new BiRefEdEntity {
                Id = 1, Data = "data_ed_1"
            };
            var ed2 = new BiRefEdEntity {
                Id = 2, Data = "data_ed_2"
            };
            var ing1 = new BiRefIngEntity {
                Id = 3, Data = "data_ing_1"
            };
            var ing2 = new BiRefIngEntity {
                Id = 4, Data = "data_ing_2"
            };

            //revision1
            using (var tx = Session.BeginTransaction())
            {
                ed1Id = (int)Session.Save(ed1);
                ed2Id = (int)Session.Save(ed2);
                tx.Commit();
            }

            //revision 2
            using (var tx = Session.BeginTransaction())
            {
                ing1.Reference = ed1;
                Session.Save(ing1);
                Session.Save(ing2);
                tx.Commit();
            }

            //revision 3
            using (var tx = Session.BeginTransaction())
            {
                ing1.Reference = null;
                ing2.Reference = ed1;
                tx.Commit();
            }

            //revision 4
            using (var tx = Session.BeginTransaction())
            {
                ing1.Reference = ed2;
                ing2.Reference = null;
                tx.Commit();
            }
        }