class hr_extra(osv.osv):
       

      _inherit = "res.partner"
      _columns = {
              
                  'date_join': fields.date('Date of Joining'),
                  'service_date': fields.date('Service Benefit Payment Date'),
                  'order_line': fields.one2many('hr.payment.line','order_id','Payment Structure'),
                  'amount_total': fields.function(_amount,string='Total', multi="sums",help="The total amount"),
      }

class payment_description(osv.osv):

      _name = 'payment.description'
      _description = 'payment Description'
      _columns = {
                  'name': fields.char('Description'),
                        
      }

class hr_payment_description_line(osv.osv):
    

    _name ='hr.payment.description.line'
    _columns = {
        'description' :fields.many2one('payment.description','Description'),
        'amount':fields.float('Amount'),
        'order_id':fields.many2one('rea.partner','Payment Details'),  
       }

I have a description & amount field in my one2many relation.

I want to sum all the values, that given in the tree structure.

Where should i call the sum ans dispaly function?

What is the code?

Please help me....

Thanks.