Using JPA to partially initialize entities

Posted on 2011-02-17
Last Modified: 2013-11-24

I have created an application with a relatively complex model. Everything was working fine and the beta-tests were running smoothly. The problem I am having is that I am using BlazeDS to send results to a Flex client. This causes all relations to be loaded (even if they are marked for lazy loading) and sent to the client. This is rather undesirable as a simple listEntityA doesn't only return a list of EntityA but also all of their references and the references of their references ... a lot of stuff.

I know in JPA I can do these really cool "SELECT NEW packagename.Classname(params...) FROM ..." to create unmanaged instances that are partially initialized (projections). The problem is, that I really would like the main entity to be fully initialized, but I would love some related objects to be only initialized with let's say "id" and "name" (all other properties left empty) ... this would be a projection of the relation.

How could I do this?
Question by:ChristoferDutz
LVL 47

Expert Comment

ID: 34915055
Would not claim that I understand much of what you are writing about, but this is the link with quite similar words,
who knows, maybe you haven't seen it:
LVL 20

Author Comment

ID: 34915254
I just added the Flex, BlazeDS, LazyCollections words in order to set the focus. My system works great without any errors. I am currently optimizing. Let me explain my problem in a little more detail

I have the following entities with the properties:

- id
- name
- oneToMany to EntityB
- oneToMany to EntityC

- id
- name
- oneToOne to EntityD

- id
- name
- (big blob of data)

- id
- name
- (big blob of data)

Open in new window

Now immagine I want to load a list of EntityA objects. When displaying one of the EntityA Objects in a list, I want to output the name of all EntityBs that are associated with that entity and output a link behind the name to switch to that entities view (I only need the id and name and not all the other properties).

So I am looking for a way to do the projection select on the related objects and not the main entity.

Expert Comment

ID: 34925099
What I understood is u want to load only the parent record but not the child record. If that is the case then you can use lazy loading

@OneToMany(mappedBy = "type", fetch = FetchType.LAZY)
    private List<Type> type= new ArrayList<Type>();
Efficient way to get backups off site to Azure

This user guide provides instructions on how to deploy and configure both a StoneFly Scale Out NAS Enterprise Cloud Drive virtual machine and Veeam Cloud Connect in the Microsoft Azure Cloud.

LVL 20

Author Comment

ID: 34925118
No ... I want to load the parent and I want to partially load the children.
I can load an entity partially by using projection in my select-statement "SELECT NEW de.cware.cweb.model.User(, FROM User usr"
What I would like to do, ist to load the parrent fully and the related entities partially in a way that in the related objects only the id and name properties are initialized.


Accepted Solution

aciuica earned 500 total points
ID: 34928956
Maybe it depends of which JPA implementation you use (if supports fields lazy loading), but annotating some fields from related entities with lazy loading can be a soution.
LVL 20

Author Comment

ID: 34954489
I'm currently stuck with an ANTLR problem ... I'l check this lazy loaded property thing you mentioned ... sounds very prommissing :-)
LVL 20

Author Closing Comment

ID: 34996366
Thanks for the tip with the lazy-loaded properties.

I actually solved my problem by going from JPA to Jdbc directly as here I could controll exactly what I wanted to do.

Thanks anyway.

Featured Post

3 Use Cases for Connected Systems

Our Dev teams are like yours. They’re continually cranking out code for new features/bugs fixes, testing, deploying, testing some more, responding to production monitoring events and more. It’s complex. So, we thought you’d like to see what’s working for us.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
diffSum example 4 37
hibernate example using maven 12 42
Querying data from 3 SQL tables 2 32
sql import cannot be resolved jsp 3 23
This article explains all about SQL Server Piecemeal Restore with examples in step by step manner.
Shadow IT is coming out of the shadows as more businesses are choosing cloud-based applications. It is now a multi-cloud world for most organizations. Simultaneously, most businesses have yet to consolidate with one cloud provider or define an offic…
Video by: Steve
Using examples as well as descriptions, step through each of the common simple join types, explaining differences in syntax, differences in expected outputs and showing how the queries run along with the actual outputs based upon a simple set of dem…
This tutorial covers a step-by-step guide to install VisualVM launcher in eclipse.

810 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question