Hi Need a help..

class AccountInvoice(models.Model):

    _inherit = 'account.invoice'

    @api.multi
    def action_invoice_open(self):
        inv_ids = super(AccountInvoice,self).action_invoice_open()
        invoice_obj_wish=self.env['wishlist.invoice.line']
        order_line_obj=self.env['sale.order.line']
        sale_order_id = self.env['sale.order'].search([('name', '=', self.name)], limit=1).id
        # env_val=

        for order_details_id in self.browse(sale_order_id):
            vals = {

                    'invoice_status':str(self.state),
                    'wishlist_invoice_id': sale_order_id,
                    'wishinv_number':str(self.number),
                    'invoice_date':self.date_invoice,
                    'invoice_id':self.id

                }

            for order_val in self.env['sale.order'].browse(sale_order_id):
                
                orderline_write = order_line_obj.search(
                    [('id', '=', self.invoice_line_ids.wish_ref.id)]) #Here I am getting Error(ValueError: Expected singleton: account.invoice.line(31, 32)) If i validate with Multiple lines

#If i validate with single line its working ...

                for line in order_val.order_line:
                    orderline_write.write({'status_wish':'invoiced_open'})

            update_val=invoice_obj_wish.search(['&', ('wishlist_invoice_id', '=', sale_order_id),('invoice_id','=',self.id)])
            update_val.write(vals)

        return inv_ids
class AccountInvoiceLine(models.Model):

    _inherit = 'account.invoice.line'

    wish_ref=fields.Many2one('sale.order.line')