ofy().save().entity(h);

@Entity
 public  class House {
    @Id
    public Long id;
    public String name;
    public Room room;
 }

 public  class Room implements IEmbeddedEntity<Room> {

    public long number;
    public String owner;

    @Override
    public EmbeddedEntity createEmbeddedEntity() {
        final EmbeddedEntity embeddedEntity = new EmbeddedEntity();
        embeddedEntity.setProperty("number", this.number);
        embeddedEntity.setProperty("owner", this.owner);
        return embeddedEntity;
    }

    @Override
    public Room setFieldsFrom(EmbeddedEntity embeddedEntity) {
        number = (Long) embeddedEntity.getProperty("number");
        owner = (String) embeddedEntity.getProperty("owner");
        return this;
    }
}