Anyone please help me,
i have a custom module related to purchase.order , i use this code to make additional tab in purchase.order here's the code :
approval.py
#I make this new form to save master data approval
class master(osv.osv):
    _name="wtc.approval.matrixbiaya"
    _columns = {
        'form':fields.many2one('ir.model',string='Form',required=True),
        'cabang_id':fields.many2one('res.partner',string='Branch',required=True),
        'divisi_id':fields.selection([('t','Unit'),('s','Sparepart'),('u','Umum'),('f','Finance')],'Division',change_default=True,required=True),
        'group_id':fields.many2one('res.groups',string='Group',required=True),
        'limit': fields.float(digits=(8,2), string="Limit",required=True),
}
#i make this code to make a new tab called 'Approval' in purchase.order
class approval_po(osv.osv):
    _inherit="purchase.order"
    _columns={
              'app_line': fields.one2many('apps.po','purchase_id',string="Table Approval"),
              }
#this code is method to generate button approval
    def wtc_approval(self, cr, uid, ids, context=None):
        res = super(approval_po, self).wtc_approval(cr, uid, ids, context=context)
        print "dffffffffffffffffffff"
        return res
# This is create method
    def create(self, cr, uid, vals, context=None):
         vit = self.pool.get("wtc.approval.matrixbiaya").search(cr,uid,[("cabang_id","=",vals["cabang_id"]), ("form","=","purchase.order"), ("divisi_id","=",vals["divisi_id"])])
        data = self.pool.get("wtc.approval.matrixbiaya").browse(cr,uid,vit)
        approval = []
        for x in data :
            approval.append({
                             'group':x.group_id.id,
                             'cabang_id':x.cabang_id.id,
                             'wewenang':x.limit,
                             'sts':'1',                             
                             })
        vals["app_line"] = approval
 
        return super(approval_po, self).create(cr, uid, vals, context=context)
#this code is table for a new tab
class approval_po_line(osv.osv):
    _name="apps.po"
    _columns={
              'purchase_id' :fields.many2one('purchase.order','Purchase'),
              'group':fields.many2one('res.groups','Group', select=True),
              'cabang_id': fields.many2one('res.partner','Branch',select=True),
              'wewenang':fields.char('Wewenang', size=128),
              'sts':fields.selection([('1','NO'),('2','OK')],'Status',change_default=True),
              'pelaksana':fields.many2one('res.users','Pelaksana'),
              'tanggal':fields.datetime('Tanggal'),
              }
    _defaults={
              'sts' : '1'
              }
---------------------------------------------------------------------------------------------------------------------------------------------------------
approval_view.xml
<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>  
    <!-- this code for a new form Mater Approval -->
<record model="ir.ui.view" id="master_approval_tree_view">
    <field name="name">master.approval.tree</field>
    <field name="model">wtc.approval.matrixbiaya</field>
    <field name="arch" type="xml">
        <tree string="Approval Matrix Biaya">
            <field name="form"/>
            <field name="cabang_id"/>
            <field name="divisi_id"/>
            <field name="group_id"/>
            <field name="limit"/>
        </tree>
     </field>
</record>
    
<record id="master_approval" model="ir.ui.view">
     <field name="name">master.approval.view</field>
     <field name="model">wtc.approval.matrixbiaya</field>
     <field name="arch" type="xml">
         <form string="Form Approval Matrix Biaya" version="7.0">
             <group>
                 <field name="form" style="width: 25%%"/>
                 <field name="cabang_id" style="width: 30%%"/>
                 <field name="divisi_id" style="width: 10%%"/>
                 <field name="group_id" style="width: 45%%"/>
                 <field name="limit"/>
            </group>
        </form>
        </field>                                                                                                                        
</record>     
<record model="ir.actions.act_window" id="approval_action">
    <field name="name">Matrix Approval Biaya</field>
    <field name="res_model">wtc.approval.matrixbiaya</field>
    <field name="view_type">form</field>
    <field name="view_mode">tree,form</field>
</record>
<!-- This code for a new Tab called 'Approval'-->
<record id="rules_approval_po" model="ir.ui.view">
    <field name="name">master_approval_po_tab</field>
    <field name="model">purchase.order</field>
    <field name="inherit_id" ref="purchase.purchase_order_form"/>
    <field name="arch" type="xml">
    
        <button name="view_picking" position="after">
            <button string="Approval" name="wtc_approval" type="object" class="oe_highlight"/>
        </button>
            <field name="partner_id" position="before">
                <field name="cabang_id"></field>
                <field name="divisi_id" style="width:35%%"></field>
            </field>
            <xpath expr="//page[@string='Deliveries & Invoices']" position="after">
            <page string="Approval">
            <field name="app_line">
            <tree string="Approval" editable="bottom">
                <field name="group" />
                <field name="cabang_id"/>
                <field name="wewenang"/>
                <field name="sts"/>
                <field name="pelaksana"/>
                <field name="tanggal"/>
            </tree>
            </field>
            </page>
            </xpath>
    </field>
</record>
<menuitem id="master_approval_menu" name="Approval Matrix Biaya" parent="base.menu_config"  action="approval_action"/>
                     
     </data>
 </openerp>
-----------------------------------------------------------------------------------------------------------------------------------------------------
when i create a new purchase order, the approval line doesn't show any record (that's what i want , and i want it to be read only it means it cannot add an item),
then when i save the current form purchase order , the approval line in Approval tab show some record that refer to Custom Form called 'Master Approval' , i got an error .. please help me
