MongoDB came with all sophisticated ObjectId generation feature, but often you just jumped the ship from relational database, and you still want an easy to read / communicate numeric identifier field which automatically increments every time new record is inserted.

One neat suggestion from MongoDB tutorial is to use a counter collection with a ‘counter name’ as its id, and a ‘seq’ field to store the last used number:

db.counters.insert({
  _id: "users",
  seq: 0
})

Then use findAndModify function to increment and obtain the next value.

db.counters.findAndModify({
        query: { _id: name },
        update: { $inc: { seq: 1 } },
        new: true
})

When developing using Spring Data MongoDB, this neat trick can be written as a simple service. Here I used the collection name as the counter name so it’s easy to guess / remember.

import static org.springframework.data.mongodb.core.query.Query.*;
import static org.springframework.data.mongodb.core.query.Criteria.*;
import static org.springframework.data.mongodb.core.FindAndModifyOptions.*;


public class CounterService {
   private MongoOperations mongo;
  
  public int getNextSequence(String collectionName) {

    Counter counter = mongo.findAndModify(
      query(where("_id").is(collectionName)), 
      new Update().inc("seq", 1),
      options().returnNew(true),
      Counter.class);
      
    return counter.getSeq();
  }
}

Counter is just a simple class representing the collection. Please beware the usage of int data type, this will limit to 2^31 entries maximum.

(collection = "counters")
public class Counter {
  @Id private String id;
  private int seq;
  /* getters & setters .. */
}

Then when inserting a new entry (with help of ), just set the id field like this before you save it

User newUser = new User();
newUser.setId(counterService.getNextSequence("users"));
newUser.setUsername(username);
newUser.setPassword(password);

userRepository.save(newUser);

You’ll get an incrementing simple numeric id each time you insert new object