Adding all ID's in an array from MongoDB with Java

Question

I wanted to add all of the ID's inside of MongoDB to an array with using Java. How do I take ID's or any data form and put in an array from JAVA?

PS: I'm newbie with nosql database structure and I'm using MongoDb 3.2

Code is so far something like this.

public void ArrayEx(){

    MongoClient mongoClient = new MongoClient("localhost",27017);
    MongoDatabase database = mongoClient.getDatabase("dbTest");
    MongoCollection<Document> collection =database.getCollection("colTest");
    MongoCursor<Document> cursor = collection.find().iterator();
    while(cursor.hasNext()) {

      //What should I add here?

    }
}

I want to reach every _id put them in array so that I can create a combobox of it. — John D.
– John D., Commented Mar 9, 2017 at 13:10
You can try MongoCursor<Document> cursor = collection.find().projection(new Document("_id", 1)).iterator(); while(cursor.hasNext()) { Document result = cursor.next(); Long id = result.getLong("_id"); // add to combobox } — s7vr
– s7vr, Commented Mar 9, 2017 at 13:32

Moi Syme · Accepted Answer · 2017-03-09 13:11:10Z

1

If you want only the ids, you can use the mongodb distinct function

List Ids = collection.distinct("_id");

answered Mar 9, 2017 at 13:11

Moi Syme

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2 Comments

John D. Over a year ago

I wanted to put them in array one by one so that I can create a combobox automatically.

waXve Over a year ago

I got the Idea from your answer, but I have to write some more code ;-) List<ObjectId> ids = StreamSupport.stream(collection.distinct("_id", ObjectId.class).spliterator(), false).collect(Collectors.toList());

Anand Undavia · Accepted Answer · 2017-03-10 07:40:48Z

0

Modify your method as follows :

public void ArrayEx() {

    MongoClient mongoClient = new MongoClient("localhost", 27017);
    MongoDatabase database = mongoClient.getDatabase("dbTest");
    MongoCollection<Document> collection = database.getCollection("colTest");
    MongoCursor<Document> cursor = collection.find().iterator();

    ArrayList<String> listOfIDS = new ArrayList<>();
    while (cursor.hasNext()) {
        listOfIDS.add(cursor.next().getObjectId("_id").toString());
    }

    String ids[] = new String[listOfIDS.size()];
    ids = listOfIDS.toArray(ids);
}

edited Mar 10, 2017 at 7:40

answered Mar 9, 2017 at 13:12

Anand Undavia

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7 Comments

John D. Over a year ago

Here's the thing, I'm using String, when I try to do with your example it says String cannot be converted to Long, after that when I change your codes with String this time it says Object cannot be converted to String, so what should I do?

Anand Undavia Over a year ago

On which line it says String cannot be converted to Long ?

John D. Over a year ago

It says on the localhost, I'm not sure in which line but probably problem occurs in here " listOfIDS.add(cursor.next().getLong("_id")); " because when I change here to String that case it says ObjectId cannot be cast to String.

Anand Undavia Over a year ago

Are you using MongoDB's default _id or you have overridden the _id to be long? I mean are you sure your _id field is long?

John D. Over a year ago

My _id field should be String, then again I cannot use String too because It says ObjectId cannot be cast to String...

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