EF导航属性会自动从已查出来的对象附加

public virtual void UpdateMaterialPurchaseOrderItem(
            ChangeDtos<MaterialPurchaseOrderItemDetailInputDto> itemDetail, Guid billId)
        {
            Ensure.NotNull(itemDetail, nameof(itemDetail));
            var materialPurchaseOrder = GetEntityById(billId);
            _materialPurchaseOrderItemInputUnitService.SaveChangeDtos(itemDetail, materialPurchaseOrder.OrderItemDetail);
            materialPurchaseOrder.OrderItemDetail.Where(a => a.Material == null).ForEach(a =>
                {
                    a.Material = _materialRepository.First(a.MaterialId);
                });
            RepositoryContext.Commit();
        }