我正在尝试使以下内容起作用：

_dbmsParentSections = FactoryTools.Factory.PdfSections
                        .Include(x => x.Children.OrderBy(y => y.Order).ToList())
                        .Include(x => x.Hint).Include(x => x.Fields)
                        .Where(x => x.FormId == FormId && x.Parent == null)
                        .OrderBy(o => o.Order)
                        .ToList();

导致异常的部分是：

.Include(x => x.Children.OrderBy(y => y.Order).ToList())

编辑：

经过进一步观察，

_dbmsParentSections.ForEach(x => x.Children = x.Children.OrderBy(y => y.Order).ToList());

（在首次Factory致电后，没有Children.OrderBy）为我完成了这项工作。