Question

I have created a ‘sequence’ collection. It has ‘name’ and ‘counter’ fields. The ‘name’ field is set to ‘Tag’ and ‘counter’ field is set to 0. Following is the code within a method that returns the next value of ‘counter’ field.

final Sequence tagSequence = mongoTemplate.findAndModify(
  new Query(Criteria.where("name").is("Tag")), 
  new Update().inc("counter", 1), 
  new FindAndModifyOptions().returnNew(true), Sequence.class);

However, this piece of code does not work. Any inputs?

I found an implementation for this here, http://dev.bubblemix.net/blog/2011/04/auto-increment-for-mongodb-with-the-java-driver/, however, I wanted to know what is wrong with this piece of code.

Answer 1

Your code works correctly provided that you have first saved the Sequence object, with the “Tag” name, in MongoDB. I’d suggest you annotate the name field with the @Id annotation. Ex.:

public class Sequence {
    @Id
    protected final String name;
    protected Long counter;

    public Sequence(String name, Long counter) {
        this.name = name;
        this.counter = counter;
    }
    public String getName() {
        return name;
    }
    public Long getCounter() {
        return counter;
    }
    public void setCounter(Long counter) {
        this.counter = counter;
    }

}

Save the object in MongoDB:

template.save(new Sequence("Tag",0L))