field Subscription of 'optical_equipment.equipment' always readonly

equipment.py

@@ -29,29 +29,10 @@ class OpticalEquipment(ModelSQL, ModelView):
     serial = fields.Char("Serial", size=None)
     health_register = fields.Char("Health Register", size=None)
 
-    subscription_history = fields.Many2Many('sale.subscription-optical_equipment.equipment', 'equipment', 'subscription', "Subscriptions")
+    subscription_history = fields.Many2Many('sale.subscription-optical_equipment.equipment',
+                        'equipment','subscription', "Subscriptions",
+                        states={'readonly': True})
     
     @staticmethod
     def get_origin():
         return None
-
-    @classmethod
-    def get_subscription_history(cls, records, names):
-        pool = Pool()
-        ids = []
-        for record in records:
-            ids.append(record.id)
-            
-        Subscriptions = pool.get('sale.subscription-optical_equipment.equipment')
-        subscriptions = Subscriptions.search([("equipment", 'in', ids)])
-        subscriptions_history_id = []
-        DICC = {}
-        
-        for subscription in subscriptions:
-            DICC[subscription.equipment.id] = subscription.id
-            
-        #raise UserError(str(type(subscriptions_history_id[0])))
-        #raise UserError(str(list(subscriptions_history_id[0])))
-        #raise UserError(str(type(subscriptions_history_id)))
-
-        return DICC

product.py

@@ -66,6 +66,7 @@ class Template(metaclass=PoolMeta):
 
     #These are measurements required for the equipments, are in this place
     # for manage of class 'product.template'
+    
     temperature = fields.Float("Temperature")
     temperature_uom = fields.Many2One('product.uom', 'Temperature UOM',
                     domain=[('category', '=', Id('optical_equipment', "uom_cat_temperature"))])

view/optical_equipment_form.xml

@@ -2,7 +2,6 @@
 <!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
      this repository contains the full copyright notices and license terms. -->
 <form>
-    <field name="subscription_history"/>
     <label name="company"/>
     <field name="company"/>
     <label name="location"/>
@@ -39,4 +38,11 @@
     <field name="health_register"/>
     <label name="origin_country"/>
     <field name="origin_country"/>
+    
+    <notebook>
+	<page string="Subscriptions" id="subscriptions_equipment">
+	    <field name="subscription_history"/>
+	</page>
+    </notebook>
+
 </form>