class hr_employee(osv.osv):
    _inherit = 'hr.employee'
    _columns = {
                'badge_number':fields.char('B/No',required=True),
                }
    
    
hr_employee()

<record model='ir.ui.view' id='hr_model_search'>
            <field name="name">hr.model.search</field>
            <field name="model">hr.employee</field>
            <field name="type">search</field>
            <field name="arch" type="xml">
               <search string="Badge Number" >
                    <field name="badge_number" />  #cannot search custom badge number
                </search>
            </field>
     </record>