Get Collections in Java from MongoDB

Question

I have a local MongoDB instance running via shell on windows 10. University provided a Java Project for us to learn about queries.

Now, I have a database ("imdb") and want to get two collections from it ("movies","tweets").

The problem is, one the one hand

List<String> test = mongo.getDatabaseNames();
System.out.println(test); //prints [admin,config,imdb,local]
...
db = mongo.getDB("imdb");
System.out.println(db.getCollectionNames()); //prints []

There seem to be no collections on imdb but

db.createCollection("movies", new BasicDBObject());

Returns a com.mongodb.CommandFailureException, stating that a collection 'imdb.movies' already exists.

So how do I ensure that Java actually "loads" the Collections? For Clarification: My goal is to have

System.out.println(db.getCollectionNames());

to print [movies,tweets] instead of []

The code trying to do an insert that is why you get already exists error, this post here might help, just comment out the line db.createCollection("movies", new BasicDBObject()); your error will go away — justMe
– justMe, Commented Jun 19, 2018 at 11:11
I don't need the Error to go away, createCollection was just do check if movies "truely" doesnt exist in "imdb". — Hereks
– Hereks, Commented Jun 19, 2018 at 11:17

C McCoy · Accepted Answer · 2018-06-19 13:35:17Z

1

You could try

Set<String> colls = db.getCollectionNames();

        for (String s : colls) {
            System.out.println(s);
        }

ref: code examples

answered Jun 19, 2018 at 13:35

C McCoy

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3 Comments

Hereks Over a year ago

I think there is little difference in printing every String of a Set or the Set in whole.

C McCoy Over a year ago

But if you try it you can see if db.getCollectionNames() is returning anything.

Hereks Over a year ago

Both should check if it returns anything. Anyhow, your suggestion doesn't print anything

Jyme · Accepted Answer · 2018-06-19 11:12:06Z

0

Which version of mongodb shell you're using

If it's before 3.0, it will return no data for db.getCollectionNames() command

ref: mongodb docs

answered Jun 19, 2018 at 11:12

Jyme

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6 Comments

Hereks Over a year ago

According to the zip file provided by university its Version 3.6

Jyme Over a year ago

And here said it's also apply if you're using WiredTiger storage engine. Can you check if it's the case.

Hereks Over a year ago

Not quiet sure how to check that, but running "show collections" in another shell returns both collections "movies","tweets". Therefore the java equivalent should work too!?

Jyme Over a year ago

Can you try this command db.serverStatus().storageEngine in the mongo shell

Hereks Over a year ago

Name = wiredTiger, supportscommittedreads = true, readonly = false, persisten = true So it seems like it does use wiredTiger storage. But show collections works nontheless on the shell

|

Alex · Accepted Answer · 2019-03-28 14:31:23Z

0

Since version 3.0 you should use MongoDatabase.listCollectionNames() method. http://mongodb.github.io/mongo-java-driver/3.8/driver/tutorials/databases-collections/#get-a-list-of-collections

MongoDatabase db = client.getDatabase(dbName);
MongoIterable<String> names = db.listCollectionNames();

answered Mar 28, 2019 at 14:31

Alex

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Comments

Grégori Fernandes de Lima · Accepted Answer · 2020-06-27 02:53:28Z

0

You can do like this:

//If you don't need connection's configures. i.e. your mongo is in you localhost at 127.0.0.1:27017
MongoClient cliente = new MongoClient(); //to connect into a mongo DB

MongoDatabase mongoDb = client.getDatabase("imdb");  //get database

MongoCollection<Document> robosCollection = mongoDb.getCollection("movies"); //get the name of the collection that you want

MongoCursor<Document> cursor =  robosCollection.find().cursor();//Mongo Cursor interface implementing the iterator protocol

    cursor.forEachRemaining(System.out::println); //print all documents in Collection using method reference

answered Jun 27, 2020 at 2:53

Grégori Fernandes de Lima

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