Adding New Field In order line Odoo 8

There is a problem in Odoo 8 while trying to add a new field in sale order line, the form simply doesn't save, I don't if anything's wrong with my code. I am attaching my code here:

The sale_view.xml:

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>



    <record id="view_order_line_tree_inherited" model="ir.ui.view">
        <field name="name">sale.order.line.tree.inherited</field>
        <field name="model">sale.order.line</field>
        <field name="inherit_id" ref="sale.view_order_line_tree"/>
        <field name="arch" type="xml">
            <xpath expr="//field[@name='name']" position="after">
                <field name='no_end_product'/>
                <field name='length'/>
                <field name='width'/>
            </xpath>
        </field>
    </record>

</data>

The sale.py:

import logging
from openerp.osv import fields, osv
from openerp import tools
from openerp.tools.translate import _



class sale_order_line(osv.osv):

    _inherit='sale.order.line'
    _columns= {
        'length': fields.float("Length"),
        'width': fields.float("Width"),
        'no_end_product': fields.integer("End Product No."),
    }

sale_order_line()

However the same code works fine in Openerp 7, I wonder what's creating a problem in Odoo 8.Any quick fix would be greatly appreciated.

Thanks And Regards, Yaseen Shareef