I am trying to add a sequence number in purchase order line .But when i create  multiple purchase order with orderline  the sequence comes from the previous purchase order.line sequence number .Here is my code ...

eg: Now sequence come for first purchase order with line is 1,2,3 .If I create another purchase order then order line sequence comes like 4,5,6.I need new order line sequence starting from 1,2,3.This is my issue .Need a help....

class purchase_order_line(osv.osv):

  _inherit = 'purchase.order.line'

_columns={

'line_no':fields.char('Line No'),

}

_defaults = {

'line_no':lambda obj,cr,uid,context:obj.pool.get('ir.sequence').get(cr, uid, 'purchase.order.line'),

}

=======================sequence.xml file

<?xml version="1.0"?>

<openerp>

<data noupdate="1">

<record id="seq_type_purchase_order_line" model="ir.sequence.type">

<field name="name">Purchase Order Line</field>

<field name="code">purchase.order.line</field>

</record>

<record id="seq_purchase_order_line" model="ir.sequence">

<field name="name">Purchase Order Line</field>

<field name="code">purchase.order.line</field>

<field name="padding">1</field>

<field name="number_increment">1</field>

</record>

</data>

</openerp>

==================================view.xml file-------

<record model="ir.ui.view" id="order form">

<field name="name">order.line</field>

<field name="model">purchase.order</field>

<field name="inherit_id" ref="purchase.purchase_order_form" />

<field name="arch" type="xml">

<xpath expr="/form/sheet/notebook/page/field/tree/field[@name='name']" position="after">

<field name="pdt_country"/>

</xpath>

<xpath expr="/form/sheet/notebook/page/field/tree/field[@name='name']" position="before">

<field name="line_no"/>

<!-- <field name="sequence_no" on_change="onchange_line(sequence_no)"/> -->

</xpath>

</field>

</record>