How to access object by _id nested in multiple arrays

Question

New MEAN.js/Mongo developer here, I'd really appreciate any insight I can get on this issue.

Here's the relevant part of the data I'm working with, from the top of the document. I'm trying to drill down to the _id field of the objects inside the pauses array so I can match it to a given value (to access a specific instance) and perform an update on the other attributes.

{
        "_id" : ObjectId("575c902078c8db620d50699e"),
        "username" : "superadmin",
        "poms" : [
            {
                "_id" : ObjectId("577a6c6c1d4ddcf805e6a4a0"),
                "pauses" : [ 
                    {
                        "_id" : ObjectId("577a6c6e1d4ddcf805e6a4a1"),
                        "momentResumed" : null,
                        "momentPaused" : ISODate("2016-07-04T14:02:22.643Z")
                    }, 
                    {
                        "_id" : ObjectId("577a6cae1d4ddcf805e6a4a2"),
                        "momentResumed" : null,
                        "momentPaused" : ISODate("2016-07-04T14:03:26.364Z")
                    }
                ],
                "momentCompleted" : null,
                "momentStarted" : ISODate("2016-07-04T14:02:20.383Z")
            }, 
            {
                "_id" : ObjectId("577a6d63bc35cf1006c05f64"),
                "pauses" : [ 
                    {
                        "_id" : ObjectId("577a6d64bc35cf1006c05f65"),
                        "momentResumed" : null,
                        "momentPaused" : ISODate("2016-07-04T14:06:28.685Z")
                    }, 
                    {
                        "_id" : ObjectId("577a6d67bc35cf1006c05f66"),
                        "momentResumed" : null,
                        "momentPaused" : ISODate("2016-07-04T14:06:31.869Z")
                    }, 
                    {
                        "_id" : ObjectId("577a6d7ebc35cf1006c05f67"),
                        "momentResumed" : null,
                        "momentPaused" : ISODate("2016-07-04T14:06:54.594Z")
                    }
                ],
                "momentCompleted" : ISODate("2016-07-04T14:07:00.455Z"),
                "momentStarted" : ISODate("2016-07-04T14:06:27.145Z")
            }
        ]
    }

Here's the aggregation query I've come up with:

{ "$match": { "_id": req.user._id } },
  { "$unwind": "$poms" },
  { "$project": {
      "_id": 0,
      "pom": "$poms"
  } },
  { "$match": { "pom._id": req.params.pomId } },
  { "$unwind": "$pom.pauses" },
  { "$project": {
      "pause": "$pom.pauses"
  } }

Unfortunately it's giving empty brackets. I'm really stumped, I've tried everything I've been able to think of. How would you return an object with a specific _id inside from inside "pauses"?

Any help or comments would be greatly appreciated.

Abdul Rehman Sayed · Accepted Answer · 2016-07-05 04:32:09Z

1

Wherever you are matching by object id. Try using this..

mongodb.ObjectID.createFromHexString(req.user._id);
mongodb.ObjectID.createFromHexString(req.params.pomId );

https://mongodb.github.io/node-mongodb-native/api-bson-generated/objectid.html

answered Jul 5, 2016 at 4:32

Abdul Rehman Sayed

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