How to spawn multiple clone of model using msg::Factory?

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I am using model spawner according this world plugin tutorial with option number three using msg::factory

  transport::NodePtr node(new transport::Node());
  node->Init(_parent->Name());
  transport::PublisherPtr factoryPub =
  node->Advertise<msgs::Factory>("~/factory");
  msgs::Factory msg;

  msg.set_sdf_filename("model://cylinder");

  msgs::Set(msg.mutable_pose(),
      ignition::math::Pose3d(
        ignition::math::Vector3d(1, -2, 0),
        ignition::math::Quaterniond(0, 0, 0)));

  factoryPub->Publish(msg)

I use this option because it let me set the spawn position. My problem is I do not know how to spawn another clone with same SDF model file using this method, I tried call factoryPub->Publish(msg) again but it seem gazebo only spawn a model per SDF model file.