Add new row editable in ng-grid Angular

Question

I want to add a new row to my ng-grid that is the only enable to be edited. I can add a new row pushing a new object into the datasource of the grid. I know that I can use cellEdit in the columnDefinitions object but I need that only the last row could be editable all the columns so if I press a button this last row is saved.

Any help or suggestions would be appreciated.