Odoo使用新的api如何使用@ api.onchange更新many2many id

Question

使用odoo new api @ api.onchange和@ api.depends如何更新many2many中的字段，其中字段由不在many2many中的另一个字段更新...即

class  rates(model.Model):
    _name  = 'rates'
    a  = field.Integer(string = 'VALUE DEPENDED ON')
    many2many = -----  that  contains  field c  
    which  i  need  updated when  a  changes  above 

示例代码非常有帮助