如何在Odoo-11中使用合作伙伴分类帐报告的功能获得期初和期末余额

Question

我想开立余下的余额使用功能在odoo-11中的合作伙伴分类帐报告中的date_from和date_to。我怎么能得到？

class OpeningBalance(models.Model):
    _inherit = 'res.partner'
    # _inherit = 'account.common.partner.report'
    def opbal(self, partner_id,date):
        query = """
                SELECT partner_id, SUM(debit) AS sumdr, SUM(credit) AS sumcr
                FROM account_move_line AS aml 
                WHERE 
                aml.partner_id = %s
                AND aml.date < '%s' %(partner_id,date)"""

        self.env.cr.execute(query)
        get = cr.fetchall()
        get[0].sumcr
        get[0].sumdr

        bal =  sumdr - sumcr
        return bal

我希望bal返回输入的最新期初余额。