Mongodb avoid duplicate entries

Question

I am newbie to mongodb. May I know how to avoid duplicate entries. In relational tables, we use primary key to avoid it. May I know how to specify it in Mongodb using java?<

Answer 1

As of Mongo's v3.0 Java driver, the code to create the index looks like:

public void createUniqueIndex() {
    Document index = new Document("fieldName", 1);
    MongoCollection collection = client.getDatabase("dbName").getCollection("CollectionName");
    collection.createIndex(index, new IndexOptions().unique(true));
}

// And test to verify it works as expected
@Test
public void testIndex() {
    MongoCollection collection = client.getDatabase("dbName").getCollection("CollectionName");

    Document newDoc = new Document("fieldName", "duplicateValue");
    collection.insertOne(newDoc);

    // this will throw a MongoWriteException
    try {
        collection.insertOne(newDoc);
        fail("Should have thrown a mongo write exception due to duplicate key");
    } catch (MongoWriteException e) {
        assertTrue(e.getMessage().contains("duplicate key"));
    }
}