How to exclude nested empty objects when saving?

[VladimirGK]

I am migrating from 1.6.1 to 2.2.10 (still using legacy options) and there seems to be discrepancy when saving a document.

Let's say I have the following.

  public class Address {
    private String number;
  }

  public class Person {
    private String name;
    private Address address;

    public void setName(String name) {
      this.name = name;
    }

    public void setAddress(Address address) {
      this.address = address;
    }
  }

  public void savePerson() {
    Person person = new Person();
    person.setName("");
    person.setAddress(new Address());
    
    datastore.save(peron);
  }

In morphia 2.2.10 the saved document will have:

{
   ....
  "person": {}
}

While in 1.6.1, the "person" field won't be saved.

I found that there is MapperOption - storeEmpty but by default it's false and related only for lists/maps/sets/arrays. Is there a way where the empty nested objects are not saved?

[evanchooly]

I'm guessing that sample doc at the bottom was meant to be address? At any rate, Morphia can't distinguish such a case. How Morphia, by way of how the driver works, persists an entity is that it writes each key/value pair in to BsonWriter. This is designed, at the driver level, to be an efficient "straight to the wire" mechanism (to simplify a little). It's designed to eliminate double writes (once to memory, then to the network) as much as possible. In order to do what you want, we'd have to serialize out that property, check the doc for emptiness, and then write it out. Fundamentally, that's much less efficient and is part of why Morphia moved away from that in 2.0.

If you would like to recreate that behavior, you can use an @PrePersist annotated method, or an EntityListener to scan and eliminate empty subdocs before Morphia hands it off to the driver to send to the server.