We have a class B which is a one2many field in a class A (parent class), when we modify a record of class B using a child view form by making some inputs inside this child form and we want to control them (ex: sum of 2 fields equal to 10),in case the control (_CONSTRAINT) returns FALSE, Can we display the error message box before quitting the view form B and when clicking on the SAVE button of the one2many form ? for the moment we have put a CONSTRAINT inside the class B unfortunately this constraint excutes when we save the record of the parent class A (too late). thank you for your help.