MongoDB Spring Data-将文档ID应用于子对象ID字段

Question

Please look at the following Mongo DB document:

@Document(collection = CitizenForumMessageDocument.COLLECTION_NAME)
public class ImageDocument {

    public static final String COLLECTION_NAME = "images";

    @Id
    private String      id;   // autogenerated 
    private Image       data; // data for the client (web, mobile...)
    private ImageMeta   meta; // for internal application work (uploader ip, etc...)

    [...] // getter, setter

}

// send as is to a client
public class Image {

    private String id;

    [...]
}

Is it possible to apply the document id to the Image id while document creation.

How I'm doing it now:

public void saveUploadedImage(Client client, ImageForm form) {

    ImageDocument doc = new ImageDocument();

    dao.save(doc); // create document cause we need an id...

    try {
        doc.setImage(createImage(form, doc.getId()));
        doc.setMeta(createMeta(client, form));
    } catch(Exception e){
        dao.remove(doc);
        return; // ugly...
    }

    dao.update(doc);
}

I could also do it by using some reflection hacks in my dao layer, but I hope there is a better solution for this issue.

Answer 1

You can use Mongo Lifycycle Events for this.

@Component
public class MongoListener extends AbstractMongoEventListener<ImageDocument>
{

  private final MongoTemplate mongoTemplate;

  @Autowired
  public MongoListener(final MongoTemplate mongoTemplate) {
    this.mongoTemplate = mongoTemplate;
  }

  @Override
  public void onAfterSave(AfterSaveEvent<ImageDocument> event) {

    ImageDocument imageDocument = event.getSource();
    if(imageDocument.getData().getId() == null) {
      imageDocument.getData().setId(imageDocument.getId());
      mongoTemplate.save(imageDocument);
    }
  }
}

I have to tell, that this is quite ugly, because for every save there will be two database calls.

But I don't see any other way to do this.