expenses_of_products/views/account_invoice.xml

<?xml version="1.0"?>
<openerp>
    <data>

      <record id="view_expense_search22" model="ir.ui.view">
           <field name="name">view_expense_search22</field>
           <field name="model">account.invoice</field>
           <field name="inherit_id" ref="account.view_account_invoice_filter" />
           <field name="arch" type="xml">
               <search>
                 <separator/>
                 <group string="">
                       <filter string="Piezas" context="{'group_by':'product_id'}"/>
                   </group>
               </search>
           </field>
       </record>



      <record id="supplier_form_inherit22" model="ir.ui.view">
            <field name="name">supplier_form_inherit22</field>
            <field name="model">account.invoice</field>
            <field name="inherit_id" ref="account.invoice_supplier_form"/>
            <field name="arch" type="xml">
                <field name="supplier_invoice_number" position="after">
                  <field name="product_id" domain="[('sale_ok', '=', 'true')]"/>
                </field>
            </field>
        </record>
    </data>
</openerp>