Mongoose/MongoDB Aggregation - $match $unwind $match not working?

Question

How would I change this archive-view-aggregation to also aggregate the from.view.archive : true?

..while preventing aggregation of duplicate messages..if the From User (sessionUser) exists in the To array, then only get one of this message..

 if (archive === true) {
  console.log('archive === ' + true);

  Models.Message.aggregate([

     // Match documents
     { "$match": {
          "to": { 
              "$elemMatch": {
                 "username": req.session.username,
                 "view.archive": true,
                 "view.bin": false
              }
          },
          "$or": messagingquery
     }},

     // Unwind to de-normalize
     { "$unwind": "$to" },

     // Match the array elements      
     { "$match": {
         "to.username": req.session.username,
         "to.view.archive": true,
         "to.view.bin": false
     }},

     // Group back to the original document
     { "$group": {
         "_id": "$_id",
         "from": { "$first": "$from" },
         "to": { "$push": "$to" },
         "message": { "$first": "$message" },
         "timesent": { "$first": "$timesent" },
         "replies": { "$first": "$replies" },
         "messaging": { "$first": "$messaging" }
     }},

     // Sort by updated, most recent first (descending)
     {"$sort": {"updated": -1}}

  ], function (err, messages) {

    if (err) {
      console.log(err);
      res.send(err);
    }

    res.json({
      messages : messages,
      sessionUser: sessionUser
    });

  });

}

The UserMessageSchema looks like this for both the From & To arrays of the MesageSchema:

var UserMessageSchema   = new Schema({
  user        : { "type": Schema.ObjectId, "ref": "User" },
  username    : String,
  view : {
    inbox       : Boolean,
    outbox      : Boolean,
    archive     : Boolean,
    bin         : Boolean
  },
  read : {
    marked      : { "type": Boolean, default: false },
    datetime    : Date
  },
    updated   : Date
});

Answer 1

I feel like I must be misunderstanding something about the situation, but it sounds like you should be able to add a simple $or in the first match stage:

{ "$match": {
    "$or" : [
        {
            "to": { 
                  "$elemMatch": {
                      "username": req.session.username,
                      "view.archive": true,
                      "view.bin": false
                  }
            }
        },
        {
            "from" : {
                "$elemMatch" : {
                    "username" : req.session.username,
                    "view.archive": true,
                }
            }
        }
    ],
        "$or": messagingquery
 }}

Duplication can't result from a $match stage, since $match filters documents based on a condition. Where is the duplication coming from and how exactly is a "duplicate" defined?