Duplicate the group by field value

Question

I am trying to execute following code:

MongoDatabase db = MongoDatabaseConnector.getDatabase();
    MongoCollection<Document> chatLogCollection = db.getCollection("chatLog");

    AggregateIterable<Document> result = chatLogCollection.aggregate(Arrays.asList(
            new Document("$group", new Document("_id", new Document("sessionId", "$sessionGUID").append("time", "$ts").append("makerID", "$makerID"))),
            new Document("$sort", new Document("time", -1)),
            new Document("$skip", skip),
            new Document("$limit", limit)
    ));

As I expected the output should not have duplicate sessionId values since I am using group by sessionId. But the problem is that the resulted output has duplicated sessionId values.

[
{
    "displayName": "Unauthenticated User",
    "sessionId": "7b60615d-5909-1bf8-e5b9-6ee55e08452d",
    "time": {
        "$date": 1499759790117
    },
    "makerID": "NA"
},
{
    "displayName": "Unauthenticated User",
    "sessionId": "0a6b5db0-fecf-a7c2-9757-67e562b7e37e",
    "time": {
        "$date": 1499840350180
    },
    "makerID": "NA"
},
{
    "displayName": "Unauthenticated User",
    "sessionId": "0a6b5db0-fecf-a7c2-9757-67e562b7e37e",
    "time": {
        "$date": 1499840353438
    },
    "makerID": "NA"
}

  ]

Here your grouping by `sessionId`, `time` and `makerId` so of course you get documents with same sessionId. The only way to get no duplicates is to group only by `sessionId` — felix, Jul 12 '17 at 07:09
Actually i am new to nosql databases.According to relational databases if we put some fields in select field it should be included in groupby field.That is why i added all required fields to display inside group by field — Kit, Jul 12 '17 at 07:14
I'm not sur to fully understand what your trying to achive here. Can you provide some samples documents from yout `chatLog` collection, and the expected output? — felix, Jul 12 '17 at 07:16
There you can see the sessionId having the duplicated values — Kit, Jul 12 '17 at 07:24
Yes I got it, but what to you expect as result of your query ? — felix, Jul 12 '17 at 07:25
I need to select displayName,sessionId,time,markerId while group by sessionId — Kit, Jul 12 '17 at 07:29

score 1 · Accepted Answer · answered Jul 12 '17 at 07:39

1

Try to group only by sessionId like this:

    AggregateIterable<Document> result = chatLogCollection.aggregate(Arrays.asList(
                new Document("$group", new Document("_id", "$sessionGUID")
                        .append("time", new Document("$first", "$ts"))
                        .append("makerID", new Document("$first","$makerID"))),
                new Document("$sort", new Document("time", -1)),
                new Document("$skip", skip),
                new Document("$limit", limit)
        ));

answered Jul 12 '17 at 07:39

felix

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new Document("$match", new Document("makerID", "user")) – Kit Jul 12 '17 at 09:08
Please can you tell me where to add this – Kit Jul 12 '17 at 09:09
When i add this to the beginning it does to make any change – Kit Jul 12 '17 at 09:13
@Kit add this at the beginning of the query, before the **`$group`** stage – felix Jul 12 '17 at 09:34
Thank you very much for you time and consideration. – Kit Jul 12 '17 at 09:43
I need to add a field to count the no of objects in each group.how to add a count field to my query – Kit Jul 12 '17 at 11:40

Duplicate the group by field value

1 Answers1