add field function last cost

__init__.py

@@ -3,10 +3,12 @@
 
 from trytond.pool import Pool
 from . import purchase
+from . import product
 
 
 def register():
     Pool.register(
+        product.Product,
         purchase.Configuration,
         purchase.Purchase,
         purchase.Line,

product.py

@@ -0,0 +1,24 @@
+# This file is part of Tryton.  The COPYRIGHT file at the top level of
+# this repository contains the full copyright notices and license terms.
+from decimal import Decimal
+from trytond.model import fields
+from trytond.pool import PoolMeta, Pool
+from trytond.modules.product import price_digits
+
+class Product(metaclass=PoolMeta):
+    __name__ = 'product.product'
+    last_cost = fields.Function(fields.Numeric('Last Cost', digits=price_digits,
+        help='Last purchase price'), 'get_last_cost')
+
+    def get_last_cost(self, name=None):
+        res = self.cost_price
+        InvoiceLine = Pool().get('account.invoice.line')
+        products = InvoiceLine.search_read([
+            ('product', '=', self.id),
+            ('invoice.state', 'in', ['posted', 'paid']),
+            ('invoice.type', '=', 'in'),
+        ], fields_names=['unit_price'], order=[('invoice.invoice_date', 'DESC')], limit=1)
+        if products:
+            res = products[0]['unit_price']
+        return res
+

product.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0"?>
+<!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
+this repository contains the full copyright notices and license terms. -->
+<tryton>
+    <data>
+
+        <record model="ir.ui.view" id="product_view_form_simple">
+            <field name="model">product.product</field>
+            <field name="inherit" ref="product.product_view_form_simple"/>
+            <field name="name">product_form_simple</field>
+        </record>
+    </data>
+</tryton>

tryton.cfg

@@ -1,8 +1,9 @@
 [tryton]
-version=6.0.3
+version=6.0.4
 depends:
     product
     purchase
     account_col
 xml:
     purchase.xml
+    product.xml

view/product_form_simple.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0"?>
+<!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
+this repository contains the full copyright notices and license terms. -->
+<data>
+    <xpath expr="/form/field[@name='cost_price']" position="after">
+        <label name="last_cost"/>
+        <field name="last_cost"/>
+    </xpath>
+</data>