Mongo panache - persist operation does not return a result of the insert operation

[Vivekanandan-gm]

The insertOne method in MongoCollection returns InsertOneResult. The persist methods in MongoOperations do use the insertOne methods mentioned above but they do not return the result. Why is it so? I do need the ObjectId's of the saved entities.

// MongoOperations.java

private void persist(MongoCollection collection, Object entity) { // This method does not return any thing
    ClientSession session = getSession(entity);
    if (session == null) {
        collection.insertOne(entity); // This method returns InsertOneResult
    } else {
        collection.insertOne(session, entity);
    }
}

[quarkus-bot[bot]]

/cc @FroMage (panache), @loicmathieu (mongodb,panache)

[loicmathieu]

The entity will be populated with the ObjectId, so if you need the ObjectId you can simply call getId().
Even if it's not that visible, this is documented in the example here: https://quarkus.io/guides/mongodb-panache#most-useful-operations

So after calling entity.persist() or repository.persist(entity) depending on the pattern you use you will have the id set in the entity.
This mimics what's done in JPA.

[Vivekanandan-gm]

I tried to get the id from the entity after persisting it and the id is not set. I'm using repository pattern and here is how my code looks. Am I missing something?

Entity.java

@Getter
@Builder
@MongoEntity(collection = "entity")
public class Entity {

  private ObjectId id;
  private String fieldA;
  private String fieldB;
}

Service.java

@Inject
EntityRepo entityRepo

@Transactional
public void test() {
  Entity entity= Entity.builder() // uses lombok builder
    .fieldA("")
    .fieldB("")
    .build();
  entityRepo.save(entity); // calls 'persist' internally
  System.out.println(entity.getId()); // prints 'null'
}

I tried to set the ObjectId manually by calling ObjectId.get() while creating my entity. This works fine. But I do not want the overhead of generating ObjectId every time before persisting an entity.

[loicmathieu]

You're missing the annotation that tells MongoDB POJO Codec (the facility we use under the cover) that it's your ID field.
You can either:

• Make your entity extend MongoEntity (even if you use the repository pattern) and remove your id field
• Add the annotation @BsonId to your id field.

[Vivekanandan-gm]

Making the entity extend PanacheMongoEntity worked. The @BsonId approach didn't work. Closing this discussion for now. I will probably look into it later.

[Vivekanandan-gm]

@loicmathieu Though this approach works, can I get to know why the approach to update the id in the entity was chosen, rather than returning the result for the persist operation?

The entity will be populated with the ObjectId, so if you need the ObjectId you can simply call getId(). Even if it's not that visible, this is documented in the example here: https://quarkus.io/guides/mongodb-panache#most-useful-operations

So after calling entity.persist() or repository.persist(entity) depending on the pattern you use you will have the id set in the entity. This mimics what's done in JPA.

Is it only because to mimic what's done in JPA?

[loicmathieu]

Yes, this is only to mimic what's done in JPA.
MongoDB with Panache is designed to be as close as possible to Hibernate ORM with Panache so we choose the mimic its features.