[IMP] purchase: add PO line to invoice

Some usability improvements. A field "Purchase Order" is added on the
invoice line, so it is much easier to make the link between the invoice
line and the PO.

On the other hand, the "Purchase Order" field which was used for
encoding help is kept empty since it is not meaningful.

addons/purchase/invoice.py

@@ -8,7 +8,8 @@ from openerp.tools.float_utils import float_compare
 class AccountInvoice(models.Model):
     _inherit = 'account.invoice'
 
-    purchase_id = fields.Many2one('purchase.order', string='Purchase Order', domain=[('invoice_status', '=', 'to invoice')])
+    purchase_id = fields.Many2one('purchase.order', string='Add Purchase Order', domain=[('invoice_status', '=', 'to invoice')],
+        help='Encoding help. When selected, the associated purchase order lines are added to the vendor bill. Several PO can be selected.')
 
     # Load all unsold PO lines
     @api.onchange('purchase_id')
@@ -61,7 +62,10 @@ class AccountInvoice(models.Model):
             if account:
                 data['account_id'] = account.id
             result.append(data)
+
+        self.invoice_line_ids = False # To avoid duplicates
         self.invoice_line_ids = result
+        self.purchase_id = False
         return {}
 
     @api.model
@@ -138,4 +142,7 @@ class AccountInvoice(models.Model):
 class AccountInvoiceLine(models.Model):
     """ Override AccountInvoice_line to add the link to the purchase order line it is related to"""
     _inherit = 'account.invoice.line'
+
     purchase_line_id = fields.Many2one('purchase.order.line', 'Purchase Order Line', ondelete='set null', select=True, readonly=True)
+    purchase_id = fields.Many2one('purchase.order', related='purchase_line_id.order_id', string='Purchase Order', store=False, readonly=True,
+        help='Associated Purchase Order. Filled in automatically when a PO is chosen on the vendor bill.')

addons/purchase/invoice_view.xml

@@ -61,8 +61,20 @@
                  <field name="purchase_id" domain="[('invoice_status', '=', 'to invoice'), ('partner_id', 'child_of', partner_id)]" attrs="{'invisible': [('state', '&lt;&gt;', 'draft')]}" class="oe_edit_only"/>
             </field>
             <xpath expr="//field[@name='invoice_line_ids']/tree/field[@name='company_id']" position="after">
-                 <field name="purchase_line_id" invisible="1"/>
+                <field name="purchase_line_id" invisible="1"/>
+                <field name="purchase_id"/>
             </xpath>
         </field>
     </record>
+
+    <record id="view_invoice_line_form_inherit_purchase" model="ir.ui.view">
+        <field name="name">account.invoice.line.form.inherit.purchase</field>
+        <field name="model">account.invoice.line</field>
+        <field name="inherit_id" ref="account.view_invoice_line_form"/>
+        <field name="arch" type="xml">
+            <field name="account_id" position="before">
+                <field name="purchase_id"/>
+            </field>
+        </field>
+    </record>
 </odoo>