partial void DeleteTheory(Theory instance);
 partial void UpdateTheory(Theory instance);
		private void detach_Theories(Theory entity)
		{
			this.SendPropertyChanging();
			entity.Lesson = null;
		}
 partial void InsertTheory(Theory instance);
		private void attach_Theories(Theory entity)
		{
			this.SendPropertyChanging();
			entity.Lesson = this;
		}