Most of the information is here: http://stackoverflow.com/questions/35659940/mongo-java-client-dbcollection-doesnt-return-whether-an-index-is-sparse-or-no

But I'll also paste below..

After recently upgrading the Java Mongo Driver from 2.6 to 3.2, I've noticed that I can no longer see if an index is sparse or not in DBCollection. On top of that, I don't think it's even creating sparse indexes.

For example:

        DBCollection entityCollection = db.getCollection("testCollectionIndex2");

        DBObject newIndex = new BasicDBObject();
        newIndex.put("field1", -1);
        BasicDBObject options = new BasicDBObject("unique", true);
        options.append("sparse", true);
        options.append("name", "testIndex");
        entityCollection.createIndex(newIndex, options);

Previously to upgrading, the following test has passed:

        entityCollection = db.getCollection("testCollectionIndex2");
        // index 0 is _id
        DBObject mongoIndex = entityCollection.getIndexInfo().get(1);
        Assert.assertEquals(Boolean.TRUE, mongoIndex.get("sparse"));

However, now the `sparse` field doesn't exist on the Index nor the returned JSON, at least as far as I can see in the Java driver.

How can I verify if an index is `sparse` now, using DBCollection?

This test is running against a 2.6 embedded MongoDB.

I'll note that I updated my test, and my test only, to use the newer classes (MongoCollection) to create and retrieve indexes, and it seems to work. So, I have to assume that this is a regression in the DBCollection classes.