Optional add () for many-to-many connection

Can I add multiple of the same objects to a many-to-many connection? The current setup I'm running gives me Error: Trying to '.add()' an instance which already exists!

every time I try to add a speaker multiple times. For example, perhaps speaker X speaks for 20 minutes, speaker Y takes over, and then its speaker X: s turns again. How can I solve this?

this is my event model:

attributes: {
   id: {
     type: "integer",
     primaryKey: true,
     autoIncrement: true
   },
   name: {
     type: "string",
     required: true
   },
   speakers: {
     collection: "speaker",
     via: 'events',
     dominant: true
   }
},
addSpeaker: function (options, cb) {
   Event.findOne(options.id).exec(function (err, event) {
     if (err) return cb(err);
     if (!event) return cb(new Error('Event not found.'));
     event.speakers.add(options.speaker);
     event.save(cb);
});

      

        
        
        
      

    

And also the speaker model:

attributes: {
name: {
  type: "string",
  required: true
},
title : {
  type: "string"
},
event: {
  model: "event"
},
events: {
  collection: "event",
  via: "speakers"
}
}