Fetch Array of key values from Mongo collection using java

Question

My Mongo collection is like:

db.user.find()
{"id":"11","name" : "a1", "age":"12", "add":"assddd"}
{"id":"11","name" : "a2", "age":"12", "add":"assddsaddd"}
{"id":"10","name" : "b2", "age":"12", "add":"assddsaddd"}

I need to fetch the data only for name and make an array.

Example I need to fetch data only for id = 11 So my output should be like:

name:[a1,a2]

My Java code is like:

//Mongo Connection
        Mongo mongo = new Mongo("localhost", 27017);
        DB db = mongo.getDB("test");

        DBCollection table = db.getCollection("user");

        BasicDBObject searchQuery = new BasicDBObject();
        searchQuery.put("id", "11");

        DBCursor cursor = table.find(searchQuery);
        DBObject resultElement = null;
        resultElement = cursor.next();

         Object son = JSON.parse(resultElement.toString());
         System.out.println(son);

        while (cursor.hasNext()) {
            System.out.println(cursor.next());
        }

How can i get particular key value pair in array here?

Alex Theedom · Accepted Answer · 2014-02-16 15:54:43Z

You will need to use the aggregate framework and group by the 'name' field and use addToSet to construct an array of those names.

db.user.aggregate(
    [
        { $match : {  id : "11" } },
        { $group : { _id : "$id", name : { $addToSet : "$name" } } }

    ])

This will give the following document:

{
    "_id" : "11",
    "name" : [ "a2", "a1"] 
}

You then use the cursor to retrieve the name field array.

EDIT

You can construct an aggregate function in Java like so:

    MongoClient mongoClient = null;

    try {
        mongoClient = new MongoClient("localhost", 27017);
    } catch (UnknownHostException e) {}

    DB db = mongoClient.getDB("test");

    DBCollection collection = db.getCollection("user");

    DBObject match = new BasicDBObject("$match", new BasicDBObject("id", "11"));
    DBObject groupFields = new BasicDBObject("_id", "$name");
    groupFields.put("name", new BasicDBObject("$addToSet", "$name"));
    DBObject group = new BasicDBObject("$group", groupFields);

    AggregationOutput output = collection.aggregate(match, group);

    Iterable<DBObject> itResult = output.results();

    for (DBObject dbo : itResult) {
        List<String> items = (List<String>) dbo.get("name");
        for(String item : items){
            System.out.println(item);
        }

    }

By using DBObjects you can build up your aggregate function. Take a look here for more details on how to do aggregate functions in Java. http://docs.mongodb.org/ecosystem/tutorial/use-aggregation-framework-with-java-driver/

Follow this code through and if anything is not clear let me know and will try to clarify it for you.

I cant change in MongoDb is there a way to access it that way in Java?

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