hibernate empty collection in component

Question

I have a component mapped using Hibernate. If all fields in the component in the database are null, the component itself is set to null by hibernate. This is the expected behavior and also what I need.

The problem I have, is that when I add a bag to that component, the bag is initialized to an empty list. This means the component has a non null value... resulting in the component being created.

Any idea how to fix this?

<class name="foo.bar.Entity" table="Entity">
<id name="id" column="id">
    <generator class="native" />
</id>

<property name="departure" column="departure_time" />
<property name="arrival" column="arrival_time" />

<component name="statistics">
    <bag name="linkStatistics" lazy="false" cascade="all" >
        <key column="entity_id" not-null="true" />
        <one-to-many class="foo.bar.LinkStatistics" />
    </bag>

    <property name="loggedTime" column="logged_time" />

    ...
</component>

A criteria with Restirctions.isNull("statistics") does return the expected values.

Please add information about the context: Who sets the component to null? Which is the component you're talking about? Which is the container? — Aaron Digulla
– Aaron Digulla, Commented May 7, 2010 at 7:14
Aaron, Hibernate leaves the component property (statistics, in Entity class) to null. — Jurgen Hannaert
– Jurgen Hannaert, Commented May 7, 2010 at 7:52
Seems to be a rather old problem but I have it as well and couldn't find any solution. Did you have any luck in the meantime? — Martin
– Martin, Commented Aug 21, 2010 at 13:08
did you look at null vs empty collections in hibernate@stackoverflow ? — Michael Pralow
– Michael Pralow, Commented Jun 27, 2011 at 22:14

sharakan · Accepted Answer · 2011-08-16 19:54:45Z

1

The basic problem here is that Hibernate can't distinguish between null collections and empty collections, so it treats them both as empty: non-null.

I suggest you change your Statistics component to an real entity instead. Then your foo.bar.Entity class has a reference, which can be null. This is not ideal because you'll have to create another table to store the Statistics entity, but if you want the null vs empty semantic distinction, that's a way to get it.

answered Aug 16, 2011 at 19:54

sharakan

6,9212 gold badges38 silver badges63 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Joshua Davis Over a year ago

Correct. The concept of collection doesn't really exist in the RDBMS so Hibernate (or any ORM) has to do something.

Mark Pope · Accepted Answer · 2011-07-06 19:35:39Z

0

I can't verify this but here's an idea:

public void setListProperty(List list) {
  if (list == null || list.size() == 0) {
    this.listProperty = null;
  } else {
    this.listProperty = list;
  }
}

Obviously not ideal but might be a workaround for you...

answered Jul 6, 2011 at 19:35

Mark Pope

11.3k11 gold badges51 silver badges59 bronze badges

1 Comment

dma_k Over a year ago

Does this approach really works for you? From my experience such tricks in setters lead to exception "another collection is already associated with session" in Hibernate (because Hibernate will remember the empty collection it intended to associate with parent entity). So the code above will work when entity became detached (session it was loaded with was closed), but will fail otherwise. Using null in getter is much better :)

Beatles1692 · Accepted Answer · 2012-02-17 09:08:20Z

0

Maybe this can help .it doesn't solve the problem of distinguishing between null and empty bag but it's a workaround. As you might know you can introduce an interceptor to your session that can intercept in certain actions like saving or updating entities then you can use this interceptor to check the state of your component and if it is empty make it null again so that hibernate won't save empty values. here's the docs.

answered Feb 17, 2012 at 9:08

Beatles1692

5,35040 silver badges70 bronze badges

Collectives™ on Stack Overflow

hibernate empty collection in component

3 Answers 3

1 Comment

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related