model字段预处理

class UserInfo(models.Model):
    open_code = CharField(max_lenth=8)

    def random_str(self):
        abc_str = 'qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM0123456789'
        code = []
        for i in range(8):
            r = random.choice(abc_str)
            code.append(r)
        code = ''.join(code)
        return code

    def save(self, force_insert=False, force_update=False, using=None,
             update_fields=None):
        self.open_code = self.random_str()
        super(Note,self).save(force_insert=False, force_update=False, using=None,
             update_fields=None)