Java & MongoDB - How to get the value of _id in a MongoDB document?

Question

I'm using the API specified here: http://api.mongodb.com/java/current/org/bson/Document.html

Here's the code I have:

Document doc = collection.find(Filters.eq("field","value")).first();
String id = (String) doc.getString("_id"); // this line throws exception

I already checked that doc has a returned Document but I cannot access the value of _id.

The error says this:

java.lang.ClassCastException: org.bson.types.ObjectId cannot be cast to java.lang.String

Answer 1

_id is an ObjectId, you should use this:

String id = doc.getObjectId("_id").toHexString();