Question

What is the best method to get the Mongo generated ID of a document inserted via Java.

The Java process inserting the documents is multi-thread, meaning that we need some atomic way to insert and return the ID of the object.

Also, if we setup a unique index, in the event that the object is a duplicate, will an ID be returned?

Thanks!

Answer 1

Generate the ObjectId early, use it in the insert, and there will no need to have the database return it to you.
ObjectId doesn’t use a shared sequence number to be unique, so it doesn’t matter if you generate one before inserting or retrieve it after.

public ObjectId createThing() {
    ObjectId result = new ObjectId();
    BasicDBObject thingToInsert = new BasicDbObject();
    thingToInsert.put('_id', result);
    //set other fields here
    collection.insert(thingToInsert);
    return result;
}