commit inicial

__init__.py

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+# -*- encoding: utf-8 -*-
+from . import models

__openerp__.py

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+# -*- encoding: utf-8 -*-
+
+{
+    "name": "Back to draft on purchase orders",
+    "version": "8.0.1.0.0",
+    "category": "Purchases Management",
+    "author": "Serv. Tecnol. Avanzados - Pedro M. Baeza - Eiru",
+    "website": "http://www.serviciosbaeza.com",
+    "contributors": [
+        "Oihane Crucelaegui <oihanecrucelaegi@avanzosc.es>",
+        "Pedro M. Baeza <pedro.baeza@serviciosbaeza.com>",
+    ],
+    "depends": [
+        "purchase",
+    ],
+    "data": [
+        "views/purchase_order_view.xml",
+    ],
+    "installable": True,
+}

models/__init__.py

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+# -*- encoding: utf-8 -*-
+from . import purchase_order

models/purchase_order.py

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+# -*- encoding: utf-8 -*-
+
+from openerp import models, api, exceptions, _
+
+
+class PurchaseOrder(models.Model):
+    _inherit = "purchase.order"
+
+    @api.multi
+    def button_purchase_draft(self):
+        # go from canceled state to draft state
+        for order in self:
+            order.order_line.write({'state': 'draft'})
+            for line in order.order_line:
+                line.procurement_ids.sudo().unlink()
+            order.write({'state': 'draft'})
+            order.delete_workflow()
+            order.create_workflow()
+        return True

views/purchase_order_view.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<openerp>
+    <data>
+
+        <record id="view_purhcase_order_form_draft" model="ir.ui.view">
+            <field name="name">purchase.order.form.draft</field>
+            <field name="model">purchase.order</field>
+            <field name="inherit_id" ref="purchase.purchase_order_form"/>
+            <field name="arch" type="xml">
+                <field name="state" position="before">
+                    <button name="button_purchase_draft"
+                            states="cancel"
+                            string="Back to draft"
+                            type="object"
+                            groups="base.group_no_one"/>
+                </field>
+            </field>
+        </record>
+
+    </data>
+</openerp>