tab 'equipment' in sale invisible with product

equipment.py

@@ -33,6 +33,8 @@ class OpticalEquipment(ModelSQL, ModelView):
                         'equipment','subscription', "Subscriptions",
                         states={'readonly': True})
     
+    current_subscription = fields.Many2One('sale.subscription')
+    
     @staticmethod
     def get_origin():
         return None

sale.py

@@ -1,6 +1,8 @@
 from trytond.pool import Pool, PoolMeta
 from trytond.model import ModelView, ModelSQL, fields
 from trytond.pyson import Eval, Bool, If
+from trytond.transaction import Transaction
+
 
 
 class SaleLine(metaclass=PoolMeta):
@@ -8,6 +10,65 @@ class SaleLine(metaclass=PoolMeta):
     __name__ = 'sale.line'
 
     address_equipment = fields.Many2One('party.address', "Direccion")
+    product_equipment = fields.Boolean("Product Equipment")
+    unit_digits = fields.Function(fields.Integer('Unit Digits'),
+        'on_change_with_unit_digits')
+
+
+    def on_change_with_unit_digits(self, name=None):
+        if self.unit:
+            return self.unit.digits
+        return 2
+    
+    @fields.depends('product', 'unit', 'quantity', 'sale',
+    '_parent_sale.party',
+    methods=['_get_tax_rule_pattern', '_get_context_sale_price',
+    'on_change_with_amount'])
+    def on_change_product(self):
+        Product = Pool().get('product.product')
+        if not self.product:
+            self.product_equipment = False
+            return
+
+        party = None
+
+        if self.sale and self.sale.party:
+            self.product_equipment = False
+            party = self.sale.party
+
+        # Set taxes before unit_price to have taxes in context of sale price
+        taxes = []
+        pattern = self._get_tax_rule_pattern()
+        for tax in self.product.customer_taxes_used:
+            if party and party.customer_tax_rule:
+                tax_ids = party.customer_tax_rule.apply(tax, pattern)
+                if tax_ids:
+                    taxes.extend(tax_ids)
+                continue
+            taxes.append(tax.id)
+
+        if party and party.customer_tax_rule:
+            tax_ids = party.customer_tax_rule.apply(None, pattern)
+            if tax_ids:
+                taxes.extend(tax_ids)
+        self.taxes = taxes
+
+        category = self.product.sale_uom.category
+        if not self.unit or self.unit.category != category:
+            self.unit = self.product.sale_uom
+            self.unit_digits = self.product.sale_uom.digits
+
+        with Transaction().set_context(self._get_context_sale_price()):
+            self.unit_price = Product.get_sale_price([self.product],
+                    self.quantity or 0)[self.product.id]
+
+            if self.unit_price:
+                self.unit_price = self.unit_price.quantize(
+                    Decimal(1) / 10 ** self.__class__.unit_price.digits[1])
+
+        self.type = 'line'
+        self.amount = self.on_change_with_amount()
+        self.product_equipment = True
 
     @classmethod
     @ModelView.button
@@ -24,7 +85,7 @@ class SaleLine(metaclass=PoolMeta):
     def view_attributes(cls):
         return super(SaleLine, cls).view_attributes() + [
             ('//page[@id="equipment"]', 'states', {
-                    'invisible': ~Eval('lines.product.equipment'),
+                    'invisible': ~Eval('product_equipment', True),
                     })]
 
 

view/optical_equipment_form.xml

@@ -20,6 +20,7 @@
     <field name="biomedical_class"/>
     <label name="calibration"/>
     <field name="calibration"/>
+    <newline/>
     <label name="mark_category"/>
     <field name="mark_category"/>
     <label name="model_category"/>
@@ -38,6 +39,8 @@
     <field name="health_register"/>
     <label name="origin_country"/>
     <field name="origin_country"/>
+    <label name="current_subscription"/>
+    <field name="current_subscription"/>
     
     <notebook>
 	<page string="Subscriptions" id="subscriptions_equipment">

view/sale_line_form.xml

@@ -8,4 +8,9 @@
 	    <field name="address_equipment"/>
 	</page>
     </xpath>
+    <xpath
+        expr="/form/notebook/page[@id='general']/field[@name='product']" position="after">
+        <label name="product_equipment"/>
+        <field name="product_equipment"/>
+    </xpath>
 </data>