Java MongoDB Pojo Custom Id Type

Question

I make a class like this

@BsonDiscrimintor
public class User {
    @BsonId
    private Integer _id;
    // some properties
    // getter & setter
}

and register to codec

ClassModel<User> userModel = ClassModel.builder(User.class).enableDiscriminator(true).build();
PojoCodecProvider pojoCodecProvider = PojoCodecProvider.builder().register(userModel).build();
pojoCodecRegistry = fromRegistries(MongoClient.getDefaultCodecRegistry(), fromProviders(pojoCodecProvider));


mongoClient = new MongoClient("localhost", MongoClientOptions.builder().codecRegistry(pojoCodecRegistry).build());
mongoDatabase = mongoClient.getDatabase("bbs").withCodecRegistry(pojoCodecRegistry);

When I try to insert

public int addOne(User user) {
    try {
        user.set_id(Db.getNextId("user"));

        userCollection.insertOne(user);
    } catch (Exception e) {
        e.printStackTrace();
    }

    return user.get_id();
}

But When I find it in mongo, its _id field type is ObjectID but not Int32. But I declared _id as Integer, Why?

Answer 1

The default type of id in MongoDB is ObjectID . It could be changed as you create table. It's not decided by the class define in java.

Actually, MongoDB would implicitly convert int to ObjectID when your code run.