only one quantity for sale

sale.py

@@ -49,16 +49,6 @@ class Sale(metaclass=PoolMeta):
                 queue_scheduled_at=config.sale_process_after):
             cls.__queue__.process(sales)
 
-    # @classmethod
-    # def get_equipments_in_lines(self, sales, equipments):
-    #     #raise UserError(str(equipments))
-    #     equipments = []
-    #     for line in sales[0].lines:
-    #         if line.product_equipment:
-    #             equipments.append(line.equipment.id)
-
-    #     return equipments
-
 class SaleLine(metaclass=PoolMeta):
     'SaleLine'
     __name__ = 'sale.line'
@@ -75,6 +65,12 @@ class SaleLine(metaclass=PoolMeta):
     unit_digits = fields.Function(fields.Integer('Unit Digits'),
         'on_change_with_unit_digits')
 
+
+    @classmethod
+    def __setup__(cls):
+        super(SaleLine, cls).__setup__()
+        cls.quantity.states['readonly'] = If(Eval('product_equipment') == True, True)
+         
     @fields.depends('product_equipment','equipment')
     def get_serial_equipment(self):
         if self.product_equipment:
@@ -106,11 +102,13 @@ class SaleLine(metaclass=PoolMeta):
             self.equipment_serial = None
             self.on_change_product()
 
-    @fields.depends('product_equipment', methods=['on_change_equipment'])
+    @fields.depends('product_equipment', 'quantity', methods=['on_change_equipment'])
     def on_change_product_equipment(self):
         if self.product_equipment == False:
             self.equipment = None
             self.on_change_equipment()
+        else:
+            self.quantity = 1