How to search a document and remove field from it in mongodb using java?

You can remove a field using $unset with mongo-java driver in this way:

    MongoClient mongo = new MongoClient("localhost", 27017);    DB db = (DB) mongo.getDB("testDB");    DBCollection collection = db.getCollection("collection");    DBObject query = new BasicDBObject("_id", "10-100-5675234");    DBObject update = new BasicDBObject();    update.put("$unset", new BasicDBObject("userId",""));    WriteResult result = collection.update(query, update);    mongo.close();

The easiest way is to use the functionality in the java driver:

Query query = new Query();query.addCriteria(Criteria.where("_id").is(new ObjectId("10-100-5675234")));Update update = new Update();update.unset("userId"); //the fields you want to removeupdate.set("putInYourFieldHere", "putInYourValueHere"); //the fields you want to addmongoTemplate.updateFirst(query, update, Device.class);

The above code assumes that your "_id" is your mongodb normal "_id" which means that the variable you are looking for must be encased in the new ObjectId().

An ugly way is to replace the old version with the new version of you document (no userid).

BasicDBObject newDocument = new BasicDBObject();newDocument.put("_type", "Device");newDocument.put("alias", "new Alias name");// ...  BasicDBObject searchQuery = new BasicDBObject().append("_id", "10-100-5675234");collection.update(searchQuery, newDocument);