How to reject an object's changes?

Good day.

NopCommerce 2.2

I'm making some changes in the categories feature and, in CategoryService.UpdateCategory method I save some info in my table (SiteCategory).

I do not call  _categoryRepository.Update(category), but, anyway, the category's changes are stored in the database. Is there way to prevent this kind of behaviour? I have no found something like RejectChanged or DetachObject for an object.

How can I store something in the database, excluding a particular (changed) object?

Thank you very much for any advices,

Serge.

UPD: Found this way:

((IObjectContextAdapter)this._context).ObjectContext.Detach(category);