class Service(models.Model):
    service_name = models.CharField(max_length=200)
    service_text = models.CharField(,max_length=200)
    access_port = models.CharField(max_length=200)
    def __str__(self):
        return self.service_name

class ServiceTag(models.Model):
    service = models.ForeignKey(Service)
    tag_version = models.CharField(max_length=200)
    def __str__(self):
        return self.service.service_name+'_'+self.tag_version

class SettingItem(models.Model):
    ipservice = models.ForeignKey(Service)
    ipenvironment = models.OneToOneField('Environment')
    host_ip = models.CharField(max_length=200)
    def __str__(self):
        return self.host_ip

class Environment(models.Model):
    project = models.ForeignKey(Project)
    environment_name = models.CharField(max_length=200)
    servicetag = models.ManyToManyField(ServiceTag)
    def __str__(self):
        return self.project.project_name+'-'+self.environment_name

请问已知了Environment和ServicreTag对象怎么获得对应的SettingItem对象啊？