请教大家，如何在销售订单子表上加字段？

[ljm]

公司是做瓦楞纸，openerp有些不适用，需求发过贴子 [检测到链接无效，已移除] br />
[b]init.py:[/b]

import wlz_order

[b]openerp.py:[/b]

# -- encoding:utf-8 --
{
"name" : "瓦楞纸行业",
"version" : "1.0",
"description" : '适用于瓦楞纸行业',
"depends" : ["sale"],
"init_xml" : [],
"update_xml" : ['wlz_order_view.xml'],
"installable" : True,
}

[b]wlz_order.py[/b]:

# -- coding: utf-8 --
#!/usr/bin/python
from osv import osv, fields

class sale_order_line(osv.osv):
    _name = 'sale.order.line'
    _inherit = 'sale.order.line'
    _description = 'Sale Order Line'
    _columns = {
      'product_swgg':fields.char('实物规格',size=8),
      'product_yjgg':fields.char('应计规格',size=8),
      'product_zs':fields.integer('张数',size=5),
      'product_mj':fields.float('面积',digits=(16,2))
  }
sale_order_line()

[b]wlz_order_view.xml:[/b]

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <record model="ir.ui.view" id="view_order_line_form">
            <field name="name">wlz.order.line.form</field>
            <field name="type">form</field>
            <field name="model">sale.order.line</field>
            <field name="inherit_id" ref="sale.view_order_line_form2"/>
            <field name="arch" type="xml">
                <field name="name" position="after">
                    <field name="product_swgg"/>
                    <field name="product_yjgg"/>
                </field>
            </field>
        </record>
       
    </data>
</openerp>